The deal can't be finalized until at least July 7, when a leaguewide moratorium is lifted on signings and trades.
Mahinmi's Twitter account had a message directed at the Wizards' account.
@WashWizards let's gooooo 💪🏾!!!!!!🙏🏾🙏🏾🙏🏾🙏🏾🙏🏾🙏🏾🙏🏾🙏🏾🙏🏾— Ian Mahinmi (@ianmahinmi) July 3, 2016
The Washington Post first reported the terms of the contract.
Mahinmi should be able to provide defense and rebounding for the Wizards. He is a 6-foot-11, 250-pound center who averaged career highs of 9.3 points, 7.1 rebounds, 1.5 assists and about 25 minutes in 71 games last season, all starts for the Indiana Pacers.
The 29-year-old Mahinmi, who is from France, was drafted in the first round by the San Antonio Spurs in 2005 and made his NBA debut in the 2007-08 season. For his career, he has averaged 5.1 points and 4.3 rebounds in less than 17 minutes.
Mahinmi is the first new player added to the Wizards since the start of free agency, although they did agree Friday to a $128 million, five-year contract that will keep shooting guard Bradley Beal with the team. Beal, who teams with John Wall to give Washington a dynamic backcourt, was a restricted free agent.
Washington made sure to clear plenty of cap space heading into this offseason, and even after the contracts for Beal and Mahinmi, the team has only seven players signed. The only other center on the roster at the moment is last season's starter, Marcin Gortat.
Last season, the Wizards went 41-41 to finish 10th in the Eastern Conference and miss the playoffs, after two consecutive trips to the second round. Randy Wittman was fired as coach and replaced by Scott Brooks.
Information from The Associated Press was used in this report.