The forward has penned a three-year contract with Matsatsantsa after turning down an offer from Platinum Stars. Dikwena initially looked to have the inside track on landing the player, but United have now won the race to his signature.
Mnyamane has already joined Stuart Baxter's side for pre-season training.
"It's a done deal. The club will make an official announcement soon," an official at SuperSport tells KickOff.com.
AmaTuks agreed to allow the 23-year-old to move on after their relegation to the National First Division last month following their failure in the playoffs.
Mnyamane was the subject of interest from Kaizer Chiefs in April last year after scoring his first goal for Bafana Bafana against Swaziland, and had also been more recently linked with Orlando Pirates.