The split follows a run of difficult form for Percat, who has qualified last for four of the last six races across the Perth and Winton weekends.
However the announcement doesn't cite performance as a reason for Slater's departure after just six months with the team, instead referencing limits on performance personnel allowed at events.
As part of an engineering re-shuffle, Head of Performance Grant McPherson – formerly Shane van Gisbergen's race engineer at Triple Eight – will take over running Percat's car for the remainder of the season.
Technical Director Carl Faux will return to the travelling crew to overseas operations on race weekends.
"Walkinshaw Andretti United can confirm the team and Geoff Slater have parted ways," read a statement provided by WAU.
"Everyone at WAU wish Geoff well for the future, and thank him for his contribution.
"With restrictions on numbers at track still in place, it’s critical to put the best team on the ground at events, which ultimately leads to tough decisions being made.
"Head of Performance, Grant McPherson, will take over the running of car #2 for the remainder of 2022, with Technical Director Carl Faux to oversee the race weekend from track.
"The Team will be making no further comment at this stage."
Slater joined WAU along with Percat for the 2022 season, however, unlike Chaz Mostert and Adam De Borre it wasn't a package deal, Percat and Slater having never worked together before.
After a reasonably promising start to the season, Percat's form has fallen away in recent rounds.
Initially there were issues on both sides of the WAU garage, both Mostert and Percat struggling for pace in Perth.
Mostert, however, was able to reclaim some form at Winton late last month while Percat continued to struggle.
