Cumbrian Maher, 25, has steadily improved his form since joining from Castleford Tigers ahead of last season.
He has played the last 15 games for Rovers and become an important member of the squad that has reached the Super League play-offs.
Maher - who stands at six foot five inches - has now signed a new, one-year extension with the Robins until the end of 2022.
Ahead of Friday's elmination play-off at Warrington Wolves, Smith said: “I’m looking forward to working with Will next year.
"I think he’s really progressed since he first joined us.
“Still, I think his best years are still to come. He knows he’s got things to work on but he’s a terrific young man and smart with the way he goes about his rugby league - both in preparation and on the field.
“He’s a pleasure to work with and he’ll face competition in the middle in 2022, but I think that will bring out the best in him.”