Houli has signed on until the end of 2018, while Grigg has signed a on-year contract extension with the club, taking him through to the end of next season.
Both players have rebuilt their career at Richmond, after joining at the end of 2010 from other clubs.
Houli played 26 games in four seasons with Essendon before joining the Tigers, where he has played 122 games.
He has made 11 appearances this season, with injury limiting his opportunity. However, he been a consistent performer, averaging 25 disposals per games off the half back line.
Grigg has played 123 games for Richmond since moving across from Carlton, where he played 43 games from 2007 to 2010.
The 28-year-old is averaging 24.6 disposals, 5.1 marks and has booted 10 goals in his 19 games this season.