The 22-year-old arrived at the Emirates in the summer of 2021 from Benfica for a reported transfer fee of £8million.
Tavares has since made 28 first-team appearances across all competitions, including 22 in the Premier League.
The Portugal U21 international scored his first goal for the Gunners in a 3-1 victory over Manchester United back in April.
Tavares will have the opportunity to play Champions League football after Marseille qualified for the tournament by finishing second in Ligue 1 last season.
The French giants finished the campaign a massive 15 points behind eventual league winners PSG.
Marseille return to Europe's elite club competition for just the second time in eight years as they look to re-establish themselves as Champions League regulars.
The club have already done business with Arsenal during this summer transfer window after sealing a permanent move for Matteo Guendouzi.
Marseille splashed £8.8million on the midfielder, who fell out of favour with Gunners boss Mikel Arteta.
The French club have also signed Lens defender Jonathan Clauss and Granada forward Luis Suarez during a busy transfer window for Igor Tudor's side.