Richards, 21, began his senior career with St Helens and has made 73 appearances for the club since 2013.
"Greg has been at an elite club for a number of years and played a lot of games," Leigh coach Neil Jukes said.
"He is going to bring good habits and plenty of experience, even though he has youth on his side."
Leigh Centurions have signed prop Greg Richards from St Helens on a deal until the end of November 2018, with an option of a further year.