The Gunners have reportedly parted with an £18m transfer fee to land the 21-year-old as their second summer signing following the capture of Nuno Tavares from Benfica.
Lokonga made 78 senior appearances for Anderlecht after breaking into the first team in 2017. He worked with former Manchester City captain Vincent Kompany for the Belgian giants last season.
Arsenal manager Mikel Arteta told the club website: “Albert is a very intelligent player who has shown great maturity in his performances during his development. He has been coached well by Vincent Kompany and his team at Anderlecht.
"I know Vincent very well and he talks so highly about Albert and the positive impact he had to Anderlecht in recent seasons. We’re confident Albert’s ready for the next stage in his development and we’re looking forward to welcoming a new member to our squad with his quality and presence.”
Technical director Edu added: "We are delighted Albert has signed with us, as there was a lot of interest in him and he was a big target for us.
"Albert is a player we've been tracking for some time, and he will bring us strength in depth in the centre of midfield. We look forward to his continued development with us."
Arsenal are also looking to add Brighton and Hove Albion defender Ben White to their ranks in the coming days.
