The former Mthatha Bucks and Polokwane City manager resigned from his post as Venda Football Academy head coach last week to make way for the move.
He led the club for their first three games of the new Motsepe Foundation Championship season, picking up one point from three matches.
The Betway Premiership club posted on social media: "Marumo Gallants FC proudly welcomes Duncan Thaane Lechesa as our new assistant coach!
"Hailing from Bloemfontein, Coach Lechesa brings a wealth of experience."
Sekhukhune United were held 1-1 by Durban City, Marumo Gallants broke a 12-match winless streak with a 3-1 win over Chippa United while AmaZulu extended their goal drought in a goalless draw with Magesi in the Betway Premiership on Wednesday evening.
Chippa United beat Durban City to improve their chances of avoiding relegation from the Betway Premiership, while AmaZulu kept their momentum going.
TS Galaxy returned to winning ways in the Betway Premiership with a convincing 2-0 victory over Marumo Gallants at Mbombela Stadium on Wednesday.
A Kwazulu-Natal derby is one of the stand-out matches of what is set to be a thrilling weekend of Betway Premiership action.
