Mayo, 24, spent the first four seasons of his career with the Memphis Grizzlies, averaging 15.2 points a game. He is set to join a radically revamped Mavs roster around Dirk Nowitzki that includes center Chris Kaman, forward Elton Brand, shooting guard Dahntay Jones and point guard Darren Collison, all added in the last five days.
The third overall pick in the 2008 draft broke the news on his Twitter account, saying, "I will be signing with dallas! #Mavsnation."
Not long after, Mavs owner Mark Cuban tweeted: "Welcome to the family OJ. We are fired up !! MFFL Mavs/Mayo Fan For Life !"
The 6-foot-4 Mayo came off the bench for the Grizzlies in each of the last two seasons and his scoring average dipped about six points below his first two seasons in the league, in which he started all 164 games.
He averaged 12.6 points last season, shooting 40.8 percent from the floor and 36.4 percent from 3-point range. Mayo could become the Mavs' starting shooting guard alongside Collison, Dallas' new acquisition in a sign-and-trade with the Indiana Pacers, or he could slip into Jason Terry's former role as the team's sixth man.
The exact terms of Mayo's deal were not known, but it is a two-year deal with a player option in the second year. The Mavs had about $4 million in cap space remaining.
The Grizzlies, who entertained trading Mayo multiple times, including last season, did not make a $7.2 million qualifying offer to Mayo, allowing him to become an unrestricted free agent.
Dallas has been careful to acquire players in the final year of their contract -- Collison, Jones and Brand -- or in the case of the only other free agent they've signed in Kaman, limit the deal to one year until now.
Mayo will become the Mavs' 11th player under contract, along with three rookies. They still have interest in re-signing free agent guard Delonte West. In the 13 months since Dallas won the 2011 championship, the roster now includes just two key pieces from that team in Nowitzki and Shawn Marion.
Cuban and president of basketball operations Donnie Nelson have rebounded swiftly with additions that could help extend the franchise's record 12-year playoff streak, while at the same time help to maintain cap flexibility that will allow them to pursue a max-contract free agent next summer.