The former Scotland captain has agreed a two-year deal to join Glasgow from Perpignan this summer, with an official announcement expected within the next week.
Grant first encountered Ritchie when the back-row forward arrived at Edinburgh straight from school in 2014, while Grant was an experienced member of Alan Solomons' squad. Ritchie's talent quickly became apparent as his career flourished, and the pair would later reunite when Grant stepped into a coaching role as Edinburgh's forwards coach following his retirement.
Reflecting on Ritchie's early days in the professional game, Grant to Scotland Rugby News: "I was there when he came into Edinburgh straight from school. And first and foremost, he's just a really good bloke, good human, good guy.
"Always was, even coming out of school, really mature in that sense of comfortable being in with pros. I think it was his first experience of men's rugby as well, but he came in and just straight away was a really good player.
"He's obviously had an amazing career so far including leading Scotland. Yeah, I couldn't say enough good things about him as a bloke."
Glasgow are set to lose six internationals this summer and Ritchie's arrival will bring significant experience to Scotstoun. He will also become the fourth player in the Warriors squad to have captained Scotland - something Grant believes will add huge value both on and off the field.
"Yeah, he's been good," Grant added. "I remember when playing with him, he was always, even though he was a young player, always had time for everyone else.
"And then when I coached him at Edinburgh, all extras and training at the end, he'd grab me and be doing drills and he'd always make sure he'd speak to the younger players as well.
"So he's always had that in him. And I think that's probably, I'd imagine it would be the same in the Scotland camps as well, that he's always aware of bringing others around and helping and learning with others as well. It wasn't just the case of give, give, give. He was open and very coachable."