Three other candidates are said to be eyeing the seat as well.
The open seat represents the Second Suffolk and Middlesex Senate District, which includes Watertown, Belmont and parts of Cambridge, Allston-Brighton, the Fenway and the Back Bay.
McCarthy said in a prepared statement that if elected to the state senate, he would serve only two terms, and would donate half of his yearly senator salary to local programs aiding senior citizens and children.
"This is not about the money or a career in public office," he said. "I'm running to be a voice for those who need a voice, for those who want a voice, and more importantly for those who have no voice."
McCarthy said that his priorities include developing job opportunities, improving state and local quality of life, and fighting for public safety and education funding.
"I have spent my entire adult life standing up and fighting for working families of the middle class," McCarthy said. "As a public employee retiree, I see day in and day out the slow demise of the middle class and the ongoing struggles that families and retirees encounter."
The election to fill the vacant senate seat is scheduled for Jan. 10. A primary run off would be held Dec. 13.