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."
Marumo Gallants coach Alex Lafitte expressed frustration with the Premier Soccer League's scheduling, even as his side earned a 1-1 draw against Kaizer Chiefs at FNB Stadium on Wednesday.
Sekhukhune United secured a late 1-0 victory over Golden Arrows in their Betway Premiership encounter at the Peter Mokaba Stadium on Saturday.
The Betway Premiership returns this week after the MTN8 semi-finals, and Tuesday's five fixtures promise excitement as clubs aim to build momentum or recover from slow starts.
After parting ways with Marumo Gallants, midfield duo Phathutshedzo Nange and Kamohelo Mahlatsi have been snapped up by Motsepe Foundation Championship outfit Leicesterfield City.
