Earlier this month, the erstwhile Netherlands international confirmed to Dutch media that he and his agent had been approached by Liverpool, despite his historical connections with the Toffees.
While Jurgen Klopp's unexpected exit made the headlines last term, the German's backroom team - Pep Lijnders, Peter Krawietz, John Achterberg and Vitor Matos - departed alongside him.
As a result, Slot brought a handful of his trusted coaches with him to Merseyside, including Sipke Hulshoff, goalkeeping coach Fabian Otte and physical performance coach Ruben Peeters, but the ex-Feyenoord boss was also keen to hire Heitinga.
While the pair had never previously worked together in a coaching capacity, Heitinga had apparently embraced the same managerial philosophy as Slot thanks to his time working under a mutual connection in Marcel Keizer at Ajax.
Following a positive period of discussions, Liverpool confirmed on Wednesday that Heitinga had been appointed to the role of assistant manager, the same role he also held for West Ham United in the 2023-24 season under David Moyes.
"John Heitinga has been appointed to Liverpool's backroom staff in the position of assistant coach," the Merseyside giants said on their official website.
"The 40-year-old becomes the latest addition to Arne Slot's staff ahead of the start of 2024-25. He now joins Slot's team in assisting Liverpool's preparations for the forthcoming campaign."
Before joining Moyes's Hammers ranks for one season, Heitinga earned admirers while caretaker manager of Ajax in the second half of the 2022-23 season, masterminding 14 victories from 22 matches.
The former defender had climbed the coaching ladder with the Amsterdam giants before briefly taking the first-team reins, following a well-travelled playing career in which he became a World Cup finalist with the Netherlands.
What are Liverpool's pre-season plans?
Liverpool's stars not in Euro 2024 or Copa America action have been put through their paces by Slot for over a week now, and the Reds are preparing for their opening friendly of the summer against Real Betis on July 27.
The Reds then cross the Atlantic for a tour of the USA, where they will take on Arsenal (August 1) and Manchester United (August 4) before returning to Anfield to host Sevilla on August 11.
The 2024-25 Premier League campaign then kicks off for Liverpool on August 17, where Slot heads to newly-promoted Ipswich Town for his first competitive match at the helm.