The Anglo-Nigerian arrived at Goodison Park in January 2017 from Charlton Athletic for €11.8 million but has failed to nail down a regular playing time.
The 20-year-old made 24 appearances for the Toffees and scored three goals in all competitions.
Everton confirmed the loan deal in a statement on its website on Wednesday, which read: "Everton winger Ademola Lookman will spend the rest of the 2017/18 season with RB Leipzig after sealing a loan move to the high-flying Bundesliga club.
“Lookman joined the Blues 12 months ago from League One Charlton Athletic and scored on his debut in the 4-0 Goodison Park victory over Manchester City.
"The England Under-21 international has agreed a deal to keep him in Germany until 30 June and joins a Leipzig team sitting fifth in the league, one point outside the top four and a Champions League qualification spot.
Lookman could make his debut when the last season’s Bundesliga runners-up visit seventh-placed Borussia Monchengladbach on Saturday.