The announcement was made at the PSL offices in Parktown on Monday morning.
Davids, who is currently holding an interim position at the Team of Choice, guided his troops to three wins in four games last month, effectively ensuring their safety from relegation.
Maritzburg beat Ajax Cape Town 2-1 at home on April 1, before suffering a defeat away to Orlando Pirates on April 11.
However, they quickly bounced back with stunning 3-1 and 3-2 victories over Baroka on April 14 and Chippa United on April 25.
The Pietermaritzburg-based side are currently in seventh position with 35 points from 27 games, and are on course to land a top eight position come May 27.
Meanwhile, Onyango, who returned from injury already two games into the month, bagged the player prize for his five consecutive clean sheets in the league, which catapulted his side to second place on the log standings.
Baroka midfielder Mxolisi Kunene also bagged the Absa Premiership Goal of the Month for March, after his stunning solo effort in the 2-2 draw against Kaizer Chiefs.
Kunene picked the ball up just inside the Chiefs half, shrugged off challenges from Willard Katsande and Lucky Baloyi, before skipping past Erick Mathoho and in between Daniel Cardoso and Tsepo Masilela to fire home the equaliser past Itumeleng Khune.
View the goal at here!