The controversial Brit joined the squad in 2020, taking on a simulator programme as part of the squad's ongoing development.
Earlier this year it was confirmed that he would continue in that role again this year, as well as joining the team trackside where possible.
However, it's now been revealed that the 22-year-old has parted ways with the company.
The split apparently took place in the days prior to the Hungarian Grand Prix.
Ticktum was recently caught making negative comments about Williams' Nicholas Latifi during an online stream.
The Brit labelled the Canadian “poo” before dismissing suggestions that his presence in F1 made him better.
“He's older than me, he paid to get there,” Ticktum shot back.
“It's not like divisions, it's not like League 1 and the Premier League, that's not how it works.
“You come up through the ranks, like, I don't know, whatever…
“Just because you don't get to Formula 1 in motorsport doesn't mean you weren't good enough to get there.”
Taking to Instagram following word of his axing from Williams emerged, Ticktum claimed the split had occurred prior to the Latifi outburst.
“Myself and Williams parted ways before the recent Latifi related incident just so people know,” he wrote.
“It wasn't announced until now as there was no option for an F1 seat in 2022 for me.
“Thankyou to [Williams Racing] for the opportunity! Hope to work together in the future!”
Ticktum was formerly a member of the Red Bull junior team, but was cut from that programme midway through 2019.
Previously, he's been served a two-year ban, one year of which was suspended, after a bizarre incident at Silverstone while competing in British Formula 4 where he passed a number of cars under Safety Car conditions only to deliberately crash into Ricky Collard.
Since his return, he's twice won the Macau Grand Prix and finished second in the 2018 FIA Formula 3 Championship.
In 2017 he was awarded the BRDC McLaren Autosport Award, and a year later named the Autosport National Driver of the Year.
Williams, which has remained silent on the matter, has Jack Aitken (reserve driver), Jamie Chadwick (development driver), and Roy Nissany (test driver) still on its books.