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 are holding their ground in the face of mounting interest in their star striker Alexander Isak, with both Liverpool and Saudi Pro League side Al Hilal circling.
Leeds United have confirmed the signing of Belgian centre-back Sebastiaan Bornauw from Wolfsburg, and he is eager to show his quality in the Premier League.
Newcastle boss Eddie Howe is growing increasingly frustrated with constant speculation surrounding his star players, particularly amid ongoing rumours about Alexander Isak's future.
Liverpool have set their sights on Newcastle United’s prolific forward Alexander Isak, with reports indicating they are preparing a new blockbuster move to bring the Swedish star to Anfield.
