ESPN reported earlier this month that Marjanovic agreed to a two-year, $7 million deal with Dallas.
Marjanovic was sent to Philadelphia from the Los Angeles Clippers before the trading deadline last season and averaged a career-high 8.1 points along with 5.1 rebounds in 22 regular-season games before helping the 76ers reach the second round of the playoffs. Philadelphia lost to eventual champion Toronto in seven games.
In four seasons, the 30-year-old Serbian has averaged 6.2 points and 3.9 rebounds. Marjanovic began his second season with Detroit and went to the Clippers in the blockbuster trade that sent Blake Griffin to the Pistons.
Marjanovic played professionally in Serbia, Russia and Lithuania before coming to the NBA. He will be one of two 7-3 Europeans with the Mavericks alongside Kristaps Porzingis of Latvia.
The Associated Press contributed to this report.