The trade can't be completed until July 10, after next season's salary cap is set, so pieces were still being discussed early Friday. But the person says the Nets will get the two perennial All-Stars, signalling the breakup of the Celtics' veteran core.
The person was granted anonymity because details of the trade were not being made public.
Nets general manager Billy King refused to comment on the deal during his press conference to discuss the drafting of Mason Plumlee.
Yahoo Sports, which first reported the talks, said the Nets would also get veteran Jason Terry from Boston and send Gerald Wallace, Kris Joseph, the expiring deal of Kris Humphries and three future first-round picks to Boston.
On the day they hosted the NBA draft, the Nets were making much bigger noise with the transaction that will send Pierce and Garnett to a new Atlantic Division home.
The Celtics already let Doc Rivers leave after acquiring a draft pick from the Los Angeles Clippers. Ray Allen departed last summer for Miami, and now the other two members of the Big Three that led the Celtics to an NBA title and within a victory of a second will soon be gone as well.
"Sort of sad," said Chicago coach Tom Thibodeau, an assistant to Rivers on the 2008 NBA champions.
"You hate to see it. I certainly hate to see them go to Brooklyn, Doc of course going to the Clippers. But that's the NBA. It's constant change, and you have to be ready to adapt. I think what Paul Pierce did for that franchise and Kevin — I think's it's good for them. They have an opportunity to continue on. Good for the Celtics, where they can start their rebuilding, and it was good for Doc."
Garnett had to waive a no-trade clause, which he had been reluctant to do previously. But the Nets hoped he would consider this time with Pierce joining him and the Celtics' best days seemingly behind them.
The Celtics tumbled down the Eastern Conference standings this season, falling all the way to the No. 7 seed and getting eliminated by the New York Knicks in the first round. They have been considering moving one or both of the veterans, and this triggers the start of a true rebuilding process.
And it provides a huge boost to the Nets at two of their weakest positions. They struggled to settle on a starting power forward all last season, and Pierce would be immune to the lengthy offensive slumps that plagued Wallace, the starting small forward.
In Pierce and Garnett, rookie coach Jason Kidd gets veteran leadership from two longtime opponents as he makes the transition to the sideline after retiring as a player last month.
AP Sports Writer Andrew Seligman in Deerfield, Ill., contributed to this report.