The 25-year-old, who joined the Robins on a two-year deal from Bradford ahead of the 2020 season, has signed a two-year extension, taking him to the end of 2023.
Ryan, who scored a try on his Super League debut last March and has started each of his club’s last four matches, is the third player to extend his stay with Hull KR, following Jez Litten and Jordan Abdull.
Hull KR coach Tony Smith said: “Ethan has shown that he is a young guy developing and doing very well.
“He’s applied himself as we hoped and wished and has shown us that he could be a really important part of our future.
“It’s all about identifying those young people with ambition and he certainly is one of those that has. I think he can go a long way in the game.”