North Shields-born Longstaff usually performs a box-to-box role in midfield, but is also capable of playing in the number ten role.

He made his Under-18 debut in April 2014 and his progress since has been rapid, with the youngster swiftly becoming a regular - and impressive - performer in the Magpies' second string.

In January 2017, Longstaff joined Scottish Premiership side Kilmarnock on loan until the end of the 2016/17 season alongside teammates Freddie Woodman and Cal Roberts.

After returning to Tyneside, his signature was in demand once again and he signed for Blackpool on loan at the start of the 2017/18 campaign. After scoring nine times in League One, he was given a chance in pre-season by Rafa Benítez in the following pre-season campaign and scored against St. Patrick's Athletic in United's opening friendly.

Longstaff made his competitive first team debut against Nottingham Forest in the Carabao Cup in August 2018, before making his Premier League debut as a second-half substitute against Liverpool at Anfield that December. His first goal for the senior side followed in an FA Cup win at Blackburn Rovers a month later, before his breakthrough campaign was halted by a knee injury in March 2019.

After returning to fitness, he remained a key part of the United squad under both Steve Bruce and Eddie Howe, netting in the famous 4-1 win over Paris Saint-Germain in the Champions League at St. James' Park.