By SABC Sport
19th March 2024
The 18-year-old midfielder has been promoted into Gareth Southgate's senior group for the first time having initially been named in the under-21s squad.
Mainoo, a former under-17 and under-19 international, has burst on to the scene at Old Trafford this season, racking up 20 appearances so far.
He joins the 25 other players who reported for duty at St George's Park on Tuesday and will get the chance to stake a claim for a possible place in the squad for the summer's European Championship.
Mainoo expressed his delight on Instagram, posting: "It's an honour to receive my first senior call up."
Southgate has had the youngster on his radar for some time and recently said at February's Nations League draw: "He's doing brilliantly.
"I'm not certain he's necessarily going to be a defensive midfielder, as such.
"He's quite a progressive player but he's had a fabulous start to his career and it will be good to monitor him as we go forward."
Stockport-born Mainoo is also eligible for Ghana and their Football Association had previously expressed interest in calling him up.
The midfielder joined United as a nine-year-old and made his debut at the start of 2023 in a League Cup game with Charlton.
He has progressed at speed and, after overcoming an injury which derailed his pre-season, has often been a starter in Erik ten Hag's starting XI.
Mainoo could make his debut when England play Brazil on Saturday or against Belgium on Tuesday.