The Williams F1 junior, who won the 2021 Aston Martin Autosport BRDC Young Driver of the Year Award, will join the French outfit for his rookie campaign.
The 18-year-old spent two years in F3, first with Rodin Carlin, where he finished 11th scoring two podiums, before moving to Prema for 2023.
The Briton finished second to Gabriel Bortoleto, having taken the most wins of any driver with four.
O’Sullivan said: “I am delighted to join forces with ART Grand Prix for the 2024 FIA Formula 2 season. The team has clearly demonstrated it has all the attributes to win, so I cannot wait to get started.
“ART have already made me feel very welcome. 2024 is set to be an exciting year and I'm ready for the challenge.”
ART currently leads both the drivers and teams’ standings in F2, with Theo Pourchaire leading the championship. Victor Martins is fifth as the highest-placed rookie.
Team principal Sebastien Philippe said: “I’m delighted about the collaboration between Zak and ART Grand Prix.
“He’s a driver we’ve been following for a long time, and he has consistently elevated his level of performance.
“His background and mindset align with ART Grand Prix’s mission of supporting young drivers to the highest levels of motorsport.
“It’s with pleasure and honour that we welcome a member of the Williams Racing Driver Academy.
“With proper winter preparation, his racing approach and adaptability should enable him to compete at the front.”
O’Sullivan began racing cars in 2019, finishing as runner-up in his inaugural Ginetta Junior campaign.
The following season, he switched to single-seaters for British F4, missing out on the title by just four points from fellow Williams junior and AMABA winner Luke Browning.
In 2021, he was crowned GB3 champion with Carlin, before moving to F3 the following season, joining the Williams Driver Academy in February 2022.
He had his first taste of F1 machinery that October as his prize for winning the Aston Martin Autosport BRDC Young Driver of the Year Award, completing a day of testing at the Silverstone Grand Prix circuit in one of Aston Martin’s AMR21 cars.
