The 27-year-old has penned a four-year deal at Elland Road as the club continues to bolster its squad ahead of the new Premier League campaign.
Born in Newcastle, England on 30 October 1997, Longstaff came through the ranks at his hometown club after joining their youth system in April 2014.
He enjoyed loan spells at Kilmarnock in the Scottish Premiership during the latter part of the 2016/17 season, and at Blackpool throughout 2017/18, gaining valuable first-team experience.
He made his competitive first-team debut for Newcastle in August 2018 against Nottingham Forest in the EFL Cup, and his Premier League bow followed later that year in a match at Anfield against Liverpool.
Over the years, Longstaff became a steady presence in the Magpies' midfield, going on to make five appearances in the UEFA Champions League.
He was also part of the Newcastle squad that won the 2023/24 EFL Cup - defeating Liverpool at Wembley and ending the club's 56-year wait for silverware.
Longstaff becomes the latest addition to a busy Leeds summer, joining Sebastiaan Bornauw, Lukas Nmecha, Jaka Bijol, and Gabriel Gudmundsson in what has been a significant recruitment drive following the club's return to the Premier League.
Newcastle United have moved quickly to secure the future of one of their brightest young players after Lewis Miley signed a new long-term contract that will keep him at the club until 2032.
Newcastle United boss Eddie Howe confirmed four departures in an emotional end-of-season afternoon at St James' Park on Sunday, with senior players and long-serving staff given a warm send-off after the final match.
West Ham United's Premier League status hangs in the balance after a disappointing 3–1 loss to Newcastle United in their penultimate game of the season on Sunday.
Former PGMOL chief and ex-FIFA referee Keith Hackett believes James Maddison could face FA scrutiny after the midfielder's outspoken reaction to Tottenham's controversial 1-1 draw with Leeds.
