The day after Lyon's second term as Saints coach was confirmed, Hawthorn announced Harvey was leaving them to rejoin him as an assistant at Moorabbin.
Harvey, one of the most famous players in St Kilda history, previously ended his club-record 383-game career under Lyon in 2008.
He also served as an assistant at St Kilda for the 2010-11 seasons, leaving the club at the same time as Lyon controversially went to Fremantle.
Harvey since has been an assistant at Collingwood and was at Hawthorn for the last two seasons.
"In recent days we have had an open and honest conversation about Harvs' desire to return to his former club given the changes that have occurred there," Hawks football boss Rob McCartney said in a statement.
Lenny Hayes, another Saints great, also returned to the club in August as an assistant coach.
Nick Dal Santo coaches their AFLW team and there is speculation Brendon Goddard could return to the club.
All were key players when Lyon coached St Kilda to the 2009-10 grand finals.
"I'd love to have a few of those guys back. Robert Harvey, he has incredible respect, I have reached out to him," Lyon said earlier on Tuesday on SEN.
"He has decisions to make.
"Brendon Goddard - he's been really public in it.
"All I want to do is get good people on the bus."
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