The Newcastle Falcons tighthead, 26, moves next season to the Championship club where his international coach still holds the club record for most appearances.
Leeds-born Shelley made 244 appearances for his hometown club between 1996 and 2006, leading the club to the Powergen Cup win at Twickenham in 2005.
After retiring, Shelley moved to Canada where he has worked in various capacities with the Canadian national side in recent years and became a mentor for Ilnicki.
He said: “I have heard lots of good things about the club and I know it has a great history. This is a chance for me to play regularly and perform consistently, which is something that appealed a lot.
“I know that forwards coach Steve Boden has got a great reputation – there are guys at the Falcons who speak highly of him – and I have spoken to Mike Shelley a lot down the years about his time at Leeds.
“He has been a mentor for me for the last six years and has been the biggest influence on my career. I speak to him regularly but I have kept it a surprise from him that I had put pen to paper with his old club. It will be strange seeing pictures of him around the place – but that will keep me in line and remind me how far I have come!”
Ilnicki is the latest recruit for James Lowes’ side in 2018-19 after they announced earlier this week the signings of Jersey Reds fly-half Brendan Cope and, from French club Nevers, scrum-half JB Bruzulier.
Ilnicki, meanwhile, played Manawatu Turbos in New Zealand’s Mitre 10 Cup before coming to England to initially join Northampton Saints although he didn’t feature
In September he signed for Newcastle and has chiefly played for their A team.
He made one Premiership appearance against Exeter Chiefs in October.
Carnegie finish off their Championship season with a home game against London Scottish on Saturday but clearly new director of rugby Chris Stirling is already well under way with his plans for 2018-19.