Onyango, 29, stays on for his fifth season with the Roughyeds having originally switched codes with Widnes back in 2006.
Coach Tony Benson said: “He’s sticking with us for less money than he could have got elsewhere. He’s very loyal. His heart is here, and he’s made a lot of friends at the club.
“I’m excited because I believe we will have two of the best wingers in the competition next season in Lucas and John Gillam. Each is a big part of the team.”
Onyango has scored 62 tries in 87 games since arriving from Widnes in 2007, and originally came to this country with the Kenyan rugby union squad for the 2002 Commonwealth Games.
He said: “Other clubs were interested, but there were many reasons why I signed for Oldham again. I wanted as little disruption as possible in my final year at university but, more than that, I like playing for Roughyeds and I’m happy here. The fans are brilliant with me. They make me feel like I’m a local lad.
“Another five years and I’ll be in for a testimonial. Seriously, if we miss out on promotion again next season I’ll be thinking about hanging up my boots.
“I’ll be 30 then and losing in a Grand Final is not a good feeling. I don’t want to go through it again. As for 2011, we’ve been arouind long enough at the top end of this division to know what to expect.
“For the first time we’ll have a full season at Whitebank and that should make a big difference to the club, the players and the fans.”