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.
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.
Mathys Tel endured a dramatic night in North London as his brilliant goal was cancelled out by a costly mistake in Tottenham Hotspur's 1-1 Premier League draw against Leeds United.
Bundesliga champions Bayern Munich have reportedly opened talks with Newcastle United over signing England international winger Anthony Gordon in the summer.
Newcastle United manager Eddie Howe has admitted results must improve quickly but insisted he still believes he is the right man to lead the club forward.
