In announcing his bid for the Democratic nomination to succeed the late senator, the multimillionaire said, "It is time for me to give back to this country and this commonwealth."

Pagliuca contrasted himself with rivals Martha Coakley and Michael Capuano, veteran politicians who serve as attorney general and congressman, respectively.

"They have experience in politics; I have experience in business," he said. "We really don't have anybody that has on-the-ground business experience."

Pagliuca made his announcement at TD Bank Garden, home of the Celtics and the Boston Bruins. It hosted the basketball team's 2008 world championship run, a record 17th in franchise history. Outside the news conference room were life-sized statutes of Celtics great Larry Bird and Bruins legend Bobby Orr.

Pagliuca also is managing director of Bain Capital, ex-Massachusetts Gov. Mitt Romney's former firm. Romney was lambasted during his 1994 Senate campaign against Kennedy for job losses attributed to Bain acquisitions, but Pagliuca vigorously defended the industry.

"It's plain and simple that jobs are created by a vibrant venture capital industry," he said. "No investor is, and no senator can be, perfect. But I promise to work tirelessly to help everyone in the commonwealth to succeed."

And while he has supported Republican candidates in the past, including Romney in his 1994 campaign against Kennedy, Pagliuca said he is a lifelong Democrat.

"You have to treat your friends (well) and be loyal to your friends. But my record will show that there's ten times the amount that's been given to Democrats, and I have Democratic values and I did something for a friend," he said.

Coakley was the first Democrat to declare her candidacy, Capuano plans to formally launch his campaign Friday afternoon during an appearance at the Omni Parker House.

State Sen. Scott Brown and Canton Selectman Bob Burr are seeking the Republican nomination.

Kennedy died Aug. 25 of brain cancer.