The 21-year-old academy graduate officially signed the five-year extension on Wednesday, according to the Press Association. The agreement reportedly quadruples the player's salary to a base figure of £120,000-a-week, supplemented by performance-related bonuses.
Mainoo has made 98 senior appearances for United since his debut in January 2023. His resurgence follows a period of uncertainty earlier this season when he fell out of favour under former head coach Ruben Amorim.
Under replacement manager Michael Carrick, Mainoo has started 12 of the last 13 Premier League matches. His improved form led to a recall to the England squad under Thomas Tuchel last month, per the Manchester Evening News.
United currently occupy third place in the Premier League table with 61 points from 34 matches. The club next faces Liverpool at Old Trafford on Sunday. Securing Mainoo represents a significant step in the club's long-term planning, with veteran midfielder Casemiro expected to depart this summer.
