Democrats won at least 32 seats in the 62-seat chamber. They trailed 31-29 with two vacancies going into Tuesday.
The vote comes after record spending on both sides and gives Democratic Gov. David Paterson, just seven months on the job, a new ally along with the Assembly.
Democrat Brian Foley had almost 59 percent of the vote over Republican Sen. Caesar Trunzo with 100 percent of precincts reporting in the 3rd District in Suffolk County.
In the 15th district in Queens, Democrat Joseph Addabbo Jr., had almost 58 percent of the vote over Republican Sen. Serphin Maltese, with 100 percent of precincts reporting.
Trunzo was first elected to the Senate in 1972; Maltese was first elected in 1988.
"Today, change begins," said Senate Democratic leader Malcolm Smith of Queens. "There is much at stake for New York families and we are committed to delivering for the people of this great state without the excessive partisanship that has stalled progress in Albany. We will rebuild New York's economy, protect middle income families, get New York working again, and make government more accountable."
Elsewhere around the state, Democrats won three traditionally Republican seats in the U.S. House, expanding their near-total dominance of the state's congressional delegation to a degree not seen since 1851. In the next Congress, New York's Democrats will outnumber Republicans 26-3.
Assembly Democrats easily maintained their supermajority.
But a slim Democratic majority in the Senate doesn't necessarily mean Democrats will have a traditional, near absolute control come Jan. 1. Three Democratic senators who were re-elected Tuesday have sided with Republicans and could be wild cards that undercut the Democratic majority.
"While our numbers will be fewer, our voice will grow louder," said Senate Republican leader Dean Skelos of Long Island. "We will continue our fight to maintain balance and ensure an accountable government that represents all of the people throughout every region of the state."
Another possible Republican loss was too close to call. GOP Sen. Frank Padavan of Queens had just over 50 percent of the vote over Democrat James Gennaro, a New York City Council member.
"Republicans have failed and it's time to have a new Democratic majority in the Senate," Smith said in an interview as the votes were counted.
"It puts a lot of pressure on the Democrats to produce and be more functional than has been the case for Albany," said Lee Miringoff of the Marist College poll. "One advantage of a divided government is you always have someone to point a finger at."
The Democrats' win means the governor, the Assembly leadership and the Senate leadership will all be Democrats from New York City.
"It will be a Senate much more responsive to the governor's priorities in terms of crisis management," said Gerald Benjamin, a political scientist and dean at the State University of New York at New Paltz. "But longer term, there's a real concern for the outside-of-New-York-City voice in the leadership. I think the Senate Democrats will have to think very hard about who the second guy is."
He said the Republican majority had been the voice of upstate and Long Island.
