Jack, 25, was due to join the club in the summer, but instead starts at Edinburgh this week as head coach Mike Blair deals with reduced numbers in his front row due to the absences of Boan Venter and Luan de Bruin.
Ahead of Edinburgh’s next match against Glasgow Warriors in the deciding 1872 Cup clash at BT Murrayfield on Saturday, May 21, Jack joins a positional group alongside Scotland internationalists WP Nel and Pierre Schoeman, and Super6 props Angus William and Harrison Courtney.
Jack told Edinburgh’s website: “I’m really excited to get started. It’ll be great getting back into a full-time environment and to get the chance to do it with Edinburgh is a big honour. It was an opportunity I jumped at.
“It’s clear from speaking to a few people who have been in and around the club that Mike, Stevie and the coaching team have made it a great environment to be a part of and I’m really looking to getting involved.
“Edinburgh is obviously a club with a great history and they’ve had had a great season. With such an experienced playing group and coaching staff, I think it’ll be a really good place to test myself. Having the opportunity to play in the URC against some of the biggest teams in Europe and South Africa will be a great challenge.
“I’ve been up to Edinburgh a few times before so to be able to play in such an amazing city is a huge pulling factor as well.”
Blair added: “We’re delighted that Jamie has been able to join us early and we’re grateful to Ampthill who’ve allowed him to get started straight away.
“Jamie has had a lot of game time in the Championship this past season – a league which is obviously really big on set-piece – and comes through as one of the strongest scrummagers at the loosehead position.
“With the injury to suffered to Boan (Venter) last month, we’re obviously a bit light up front, so it’s great that Jamie can come in and help push on the other young looseheads at the club in Harrison Courtney and Sam Grahamslaw."