Fabrizio Romano confirmed the agreement on Tuesday, saying: "Kobbie Mainoo and Manchester United together for the next five years is here we go. The agreement is done over a new contract and is set to be signed in the upcoming days."
Sky Sport Germany's Florian Plettenberg separately confirmed the deal includes no release clause — a significant detail given the interest from Chelsea and Napoli that had surfaced during his period of uncertainty under former manager Ruben Amorim earlier this season.
Mainoo, who came through the United academy and made his senior breakthrough in the 2023-24 campaign, will quadruple his wages from the current figure of approximately £20,000 per week to around £120,000 per week.
He had been close to joining Napoli on loan in January when Amorim repeatedly left him out of the starting lineup, fearing it would end his World Cup hopes. Michael Carrick's appointment changed everything — Mainoo has started all but one match since January and has been one of the key figures in the club's rise to third in the Premier League.
Carrick said after Monday's 2-1 win over Brentford: "He has so much quality in build-up play, his taking of the ball, his creation and starting attacks. He's a big part of what we're doing."
Chelsea had also been monitoring Mainoo's situation and were prepared to make an approach had he become available. United are now able to plan around him as the central figure in their midfield rebuild, with Casemiro departing in June.