The former New Zealand centre, in his second season a Rovers since joining from Newcastle Knights, has extended his stay until the end of 2022.
Kenny-Dowall, 33, has been in superb form this season, forming a potent left-edge with Steve Prescott Man of Steel frontrunner Jordan Abdull, Australian back-row Kane Linnett and England winger Ryan Hall.
Robins boss Tony Smith believes the player - an NRL Grand Final winner with Sydney Roosters in 2013 - thoroughly deserves his extension.
“He has put in everything, and he has been great for us," said Smith, Kenny-Dowall being the top offloader in Super League this season with 26 as well as being in the top-five for carries (152) and top-ten for metres (1160) and tackle busts (35).
"He applies himself, he’s professional. When he speaks everybody listens because he is so respected, but he is good fun as well.
“He leads the way. He’s not always at the front of some of the things that we do but he is trying to be, and often he is up in the top group."
A 2010 Four Nations winner, Kenny-Dowall will be 34 when next season starts but - given the quality of his performances - that matters little to Smith.
“I don’t think age is as big a thing as it used to be," he said.
"For guys who look after themselves and, particularly from an early age, you can see that they play well into their mid to late thirties.
"Shaun has been in that category for most of his career and that enables him to still produce.
“He’s been terrific. I would hope if he was on the right side, he would be just as good, but he has really enjoyed moving over to that left edge (this season), and he has played a lot of his career over there.
"He’s comfortable there but he is aspiring to get better.”
Kenny-Dowall came in for some criticism during his first season at Hull College Craven Park and Smith conceded: "It was tough for him last year.
"But I think it’s hard to judge a bloke on what happened last season in the circumstances that were presented to everybody but particularly somebody who has come across from overseas.
“Not many overseas players know how tough Super League is until they throw themselves into it. It’s a different style, game and sport almost, so I think it’s hard for them to come over to adjust.
"They are often better in their second season compared to their first."