ALBANY – Buffalo Mayor Byron Brown is out as the state Democratic Party’s chairman and will be replaced by the head of the Nassau County Democratic Party, according to a source close to the party.

The state party chairman is handpicked by Gov. Andrew M. Cuomo, the state’s top party official.

Monday, he will announce his selection of Jay Jacobs, who served as party leader in the early years of the Cuomo administration.

“These are really consequential times and I believe it’s incumbent upon all of us in the Democratic Party to make sure we are as strong and united as ever before. We’re going to be organized. The governor wants a vibrant, active state party to take on the battles coming up with the elections ahead of us,’’ Jacobs said in an interview.

Jacobs and a source close to the party confirmed the change in party chairmanship. The decision by Cuomo was first reported by the New York Daily News.

Cuomo made it official shortly after 9 Monday morning, saying of Jacobs that he is “excited to work with him to further strengthen our party and elect even more Democrats up and down the ballot.’’