According to ESPN, the 29-year-old Hanson pitched five seasons in the major leagues, four with the Braves and one with the Los Angeles Angels in 2013 following a trade.
A group of Hanson's former teammates was nearby when he died at Piedmont Hospital in Atlanta, a Braves representative told MLB.com.
Hanson had been in a coma, according to multiple reports.
A source told WSB-TV, the ABC affiliate in Atlanta, that Hanson had trouble breathing early Sunday morning and was taken to a hospital. He suffered catastrophic organ failure, multiple sources told the TV station.
Hanson was selected by the Braves in the 22nd round of the 2005 draft and once was considered the top prospect in the organization.
However, after posting a 2.89 ERA over 21 starts in his rookie season of 2009, Hanson slipped each season thereafter. He saw a gradual decline in his velocity and dealt with shoulder issues that kept him on the disabled list in 2011.
He made multiple comeback attempts, with the Texas Rangers, Chicago White Sox and San Francisco Giants, but never caught on with a team.
He was 49-35 with a 3.80 ERA for his career.
MLB players, teams and fans took to social media to express their condolences.
The Braves posted this message to Twitter:
Players from the Braves and other MLB teams posted their own messages about Hanson:
Very sad to hear about Tommy Hanson. Wish his family and close friends a lot of strength. He was a really nice dude. :/— Andrelton Simmons (@Andrelton) November 10, 2015
Thoughts and prayers to the family of Tommy Hanson. Great guy and competitor. RIP— Josh Reddick (@RealJoshReddick) November 10, 2015
Very sad to hear the news about Tommy Hanson..best pitcher I saw in the minor leagues..please keep his family and friends in your prayers— David Price (@DAVIDprice14) November 10, 2015
Even other teams posted messages:
Sending our thoughts to former #Angels SP, Tommy Hanson, at this time.— Angels (@Angels) November 10, 2015
The Nationals send our deepest condolences to the family, friends and teammates of Tommy Hanson.— Washington Nationals (@Nationals) November 10, 2015
And fans are expressing their sadness for Hanson's passing:
Always sad to hear of anyone passing away, especially at a young age. Rest in peace Tommy Hanson— Cards Baseball (@TheCardsStl) November 10, 2015
At 29, most of the road is still supposed to be in front of you. RIP, Tommy Hanson.— Will (@Sharkfinhat) November 10, 2015
Our thoughts and prayers go out to Tommy Hanson's friends and family. May God bless them all. pic.twitter.com/WLsnQTEuQ7— Forever Braves (@Braves_Favs) November 10, 2015
Post your condolences for Hanson in the comment section below.
IN MEMORIAM 2015: Celebrities and notable figures who have died