Onyekuru, who made his international debut for Nigeria earlier this year, has signed a five-year deal with the Blues, initially confirming the move on his Instagram account on Tuesday evening (27 June).
Everton have not disclosed the specific fee for their latest acquisition but reports suggest the deal has set them back £7m.
The signing of another top young talent has understandably excited Everton supporters, but they will have to wait to see Onyekuru ply his trade at Goodison Park. The versatile forward will spend next season on loan with Belgian giants Anderlecht before returning to Merseyside top fight for a place in Ronald Koeman's side.
West Ham United were very interested in signing the talented forward who finished last as the top scorer in Belgium's top-flight with 22 goals for Eupen and were believed to be close to a deal last month. Arsenal were also monitoring Onyekuru, but Everton moved quickly to secure the starlet's services and make him the latest part of their summer recruitment drive.
Everton have already signed goalkeeper Jordan Pickford and Netherlands international Davy Klaassen this summer and also have a deal in place for Malaga forward Sandro - a move that will be officially confirmed on Monday, according to the Liverpool Echo.
The Blues have been uncharacteristically proactive during the close-season so far but Koeman and co are not resting on their laurels and are expected to press on with further signings.
The former Southampton boss is hoping to conclude a £25m deal for Burnley defender Michael Keane before the start of pre-season next week, while free agent Cuco Martina is expected to sign for Everton when his contract with the Saints expires on 1 July.