As he enters the White House, he's taking steps towards keeping that promise -- assembling a historically diverse slate of top-level nominees.
Half of the president-elect's Cabinet picks are women, and the majority are people of color. Biden has noted that many of his selections would be pioneers in their roles -- including the first woman to serve as treasury secretary, the first Black defense secretary, the first openly gay man confirmed to a Cabinet role and the first Native American Cabinet secretary.
But before the nominees can break barriers, they'll have to get through the confirmation process in a closely divided Senate.
Here's a look at Biden's picks for the top posts in his administration:
Department of Justice
Biden nominated Judge Merrick Garland to serve as the nation's next attorney general on Jan. 7.
Garland, 68, serves as a judge on the U.S. Court of Appeals for the D.C. Circuit. He had been nominated to the Supreme Court in 2016 by President Barack Obama to fill the vacancy left by Justice Antonin Scalia, but was never given a confirmation hearing by Senate Republicans who held the vacancy open for President Donald Trump to fill.
Garland's nomination came as Democrats won two Senate races in Georgia, paving the way to a smoother confirmation process for Biden's nominees.
Department of Labor
Biden announced Boston Mayor Marty Walsh as his nominee for labor secretary on Jan. 7.
Walsh, 53, has served as the Democratic mayor of Boston since 2014. The pro-union politician had previously served as head of the Boston Trades Council. Biden spoke at Walsh's 2017 mayoral inauguration and they share Irish-American backgrounds.
Biden said he seriously considered Vermont Sen. Bernie Sanders for the role but that both decided it was more important for their advancement of a shared political agenda to keep Sanders in the Senate.
Department of Commerce
Biden announced he'd nominate Rhode Island Gov. Gina Raimondo to commerce secretary on Jan. 7
Raimondo, who was first elected governor in 2014 and chaired the Democratic Governors Association in 2019, was one of the women under consideration to be Biden's running mate and was a potential choice to lead the Department of Health and Human Services.
Department of Education
Biden announced Miguel Cardona as his nominee to head the Department of Education on Dec. 22.
Cardona currently serves as Connecticut's commissioner of education -- the first Latino to hold the position. A former public school teacher and student, he is a strong advocate for public education.
Environmental Protection Agency
Biden announced Michael Regan as his nominee to head the EPA on Dec. 19.
Regan is no stranger to the agency, having previously served nearly a decade there under both Democratic and Republican presidents. He would be the first African American man to run the EPA if confirmed.
Regan is currently secretary of the North Carolina Department of Environmental Quality.
Department of the Interior
Biden nominated New Mexico Rep. Deb Haaland to lead the Department of the Interior.
If confirmed, she would be the first Native American Cabinet secretary.
At an event on Dec. 19 announcing his latest nominees, Biden noted the significance of having Haaland fill "a critical role."
"As the first Native American Cabinet secretary in the history of the United States of America, she'll be a true steward of our national parks, our natural resources and all of our lands," he said. "The federal government has long broken promises to Native American tribes who have been on this land since time immemorial. With her appointment, Congresswoman Haaland will help me strengthen the nation-to-nation relationship."
Department of Transportation
The president-elect announced on Dec. 15 he would nominate Pete Buttigieg to steer the Department of Transportation.
At 38, Buttigieg is the youngest of Biden's Cabinet picks so far. He is also poised to become the first openly gay person confirmed by the Senate to a Cabinet post.
Buttigieg is the former mayor of South Bend, Indiana. He ran against Biden in the Democratic primary and is seen as a rising star in the party.
As transportation secretary, Buttigieg would likely play a key part in implementing Biden's ambitious infrastructure plan, which aims to offset the impacts of climate change.
Department of Energy
Biden named former Michigan Gov. Jennifer Granholm as his selection to head the Department of Energy on Dec. 17.
Granholm led the Wolverine State during the Great Recession, working with the Obama administration to rescue the U.S. auto industry while promoting investments in green energy.
Granholm has been a strong advocate of zero-emissions vehicles and her selection is seen as an indication that Biden wants the department to play a principal role in fighting climate change.
If confirmed by the Senate, Granholm -- an immigrant from Canada -- would be just the second woman to serve as secretary of energy.
Department of Defense
Biden announced on Dec. 8 he will nominate retired four-star Army Gen. Lloyd Austin to lead the Department of Defense.
Austin previously headed the military's Central Command, where he was in charge of all American troops in the Middle East. He retired from the military in 2016, after over four decades of service. Because he is less than seven years removed from active duty, he will require a waiver from Congress to hold the position.
If Austin is confirmed, he will become the first Black defense secretary in American history.
Department of Agriculture
Biden, on Dec. 10, announced he will nominate former Iowa Gov. Tom Vilsack to serve as his secretary of agriculture.
Vilsack led the department for eight years during the Obama administration after he was unanimously confirmed by the Senate in 2009. Prior to that, he served two terms as governor of the Hawkeye State, and he is currently chief executive of the U.S. Dairy Export Council.
Vilsack would be the second member of the Obama administration to reprise their role in Biden's White House, joining the president-elect's nominee for surgeon general, Vivek Murthy, in returning to their former posts if they are both confirmed by the Senate.
Department of Housing and Urban Development
Biden announced on Dec. 10 he will nominate Ohio Rep. Marcia Fudge to serve as his secretary of housing and urban development.
Fudge is a member of the House Agriculture Committee and Committee on Education and Labor. She is a former chair of the Congressional Black Caucus and was recently elected to a seventh term in Congress, representing the Cleveland area.
Amid the recession brought on by the pandemic, millions of Americans are struggling to pay rent, and federal eviction protections set to expire at the end of 2020. If confirmed by the Senate, Fudge may be forced to grapple with a housing crisis as she takes office.
Department of Veterans Affairs
Denis McDonough, who served as former President Barack Obama's chief of staff in his second term, will be nominated, Biden said on Dec. 10, to serve as his secretary of veterans affairs.
McDonough was previously Obama's principal deputy national security adviser, including during the 2011 Navy SEAL raid that killed Osama bin Laden. Prior to his eight-year White House tenure, McDonough served in senior leadership and policy-making positions in both chambers of Congress.
He's credited with helping Obama bridge divides on Capitol Hill, including gaining support for the Veterans Choice Act which President Donald Trump later signed into law.
Department of Health and Human Services
On Dec. 6, the president-elect announced he tapped California Attorney General Xavier Becerra to steer the Department of Health and Human Services, a critical role overseeing the implementation of the Biden administration's coronavirus response.
As California's top prosecutor, Becerra took on the Trump administration in more than 100 lawsuits on key issues like health care, immigration, gun control and environmental policies. Before becoming the state's attorney general, he served 12 terms in Congress, representing Los Angeles.
Becerra does not have a background in medicine or public health, but he has established himself as advocate for the Affordable Care Act and women's health care.
Becerra, the son of Mexican immigrants, would be the first Latino to lead the department, if confirmed.
Department of Homeland Security
As part of a rollout of major foreign policy and national security appointments and nominees, the president-elect announced he would nominate Alejandro Mayorkas for secretary of homeland security on Nov. 23.
Mayorkas was born in Havana and came to the United States as a refugee. If the Senate votes to confirm him to the position, he would be the first Latino and the first immigrant to lead the agency in charge of implementing the nation's immigration policies and border laws.
Mayorkas is a veteran of the department; he directed its legal immigration agency and previously served as the deputy secretary of homeland security. He is also one of the architects behind the Deferred Action for Childhood Arrivals program (DACA).
Department of State
On Nov. 23, Biden tapped Antony Blinken as his choice for secretary of state.
Blinken has advised the president-elect on foreign policy for almost two decades. Previously, he served as deputy national security adviser and deputy secretary of state during the Obama administration.
As the country's top diplomat, Blinken would be expected to play a pivotal part in the Biden administration's efforts to rebuild alliances and reenter international agreements like the Iran nuclear deal and the Paris Climate Accord, as well as halt the country's exit from the World Health Organization.
Department of Treasury
On. Nov. 30, Biden named former Federal Reserve Chair Janet Yellen as his selection for treasury secretary. Yellen would be the first woman to serve in the role.
Yellen is currently an economist at the Brookings Institution. She was the first woman to helm the Fed, taking the reins in 2014 as the country recovered from the Great Recession.
A labor expert, Yellen is expected to garner support from progressives. A handful of Senate Republicans who are still in the chamber voted to confirm Yellen to her previous post at the central bank.
If confirmed as treasury secretary, Yellen would enter the post during one of the most trying economic times in modern history, with millions of Americans out of work due to the coronavirus pandemic and lagging job growth.
Director of the Office of Management and Budget
As part of a rollout of his incoming economic leaders, Biden announced on Nov. 30 he would nominate Neera Tanden to serve as director of the Office of Management and Budget.
A former aide to Hillary Clinton, Tanden currently serves as president and CEO of the left-leaning Center for American Progress. She faces an uphill confirmation battle as some Senate Republicans have already indicated her nomination won't pass the chamber's GOP majority, citing her past criticisms of Republican senators whose votes she would need.
If confirmed, Tanden would be the first woman of color and first South Asian American to lead the OMB.
Director of National Intelligence
Biden announced on Nov. 23 that he would nominate Avril Haines as his director of national intelligence.
Haines is a former deputy director of the CIA, and served as principal deputy national security adviser under former President Barack Obama. She was the first woman to hold both of those roles.
If confirmed, she will become the first woman to lead the country's intelligence community.
National Security Adviser
Biden said he would appoint Jake Sullivan as his national security adviser on Nov. 23.
Sullivan previously served as deputy assistant to Obama and as national security adviser to Biden when he was vice president. He's also a former top aide to Hillary Clinton.
At 43, Sullivan would be the youngest person to hold the position since the Eisenhower administration.
This role does not require Senate confirmation.
Special Presidential Envoy for Climate
Biden said he would name former Secretary of State John Kerry as his special presidential envoy for climate on Nov. 23. The newly created role marks the first time the National Security Council will include an official dedicated to climate change.
The Biden transition team did not immediately provide details on what responsibilities the position would entail, but Kerry comes with an extensive resume.
As secretary of state, Kerry negotiated the Paris Climate Accord that was signed in 2016. A longtime Massachusetts senator, Kerry also advocated for climate reform on Capitol Hill. In 2004, he was the Democratic presidential nominee.
This position does not require Senate confirmation.
US Ambassador to the United Nations
Biden announced he would nominate Linda Thomas-Greenfield for U.S. ambassador to the United Nations on Nov. 23.
Thomas-Greenfield was assistant secretary of state for Africa during the Obama administration. She has served in the Foreign Service for more than three decades.
If confirmed, she would be only the second black woman to ever hold the post.
Vice President-elect Kamala Harris will be sworn into office on Jan. 20, 2021.
Before she was elected to represent California in the U.S. Senate, she served as the state's attorney general. She ran against Biden in the 2020 Democratic primary race.
She's the first Black woman and first South Asian American to be elected to the second highest office in the land.
Biden announced he had tapped longtime adviser Ron Klain as his White House chief of staff on Nov. 11.
Klain served as Biden's chief of staff during his vice presidency. He also led the Obama administration's response to the Ebola outbreak.
This post does not require Senate confirmation.