Christiansen parted company with the club after 35 games in charge, paying the price for a run of form which was threatening to end United’s bid to reach the Championship play-offs.
Leeds slipped seven points adrift of sixth place in the table after a 4-1 defeat to Cardiff City on Saturday, their sixth league game without a win.
Christiansen, who came to Elland Road on a two-year contract last summer, saw sections of the Elland Road crowd turn on him towards full-time and admitted after the game that his position might be under threat. He parted company with United on Sunday evening.
Leeds are understood to have held concerns about both the squad’s results and a disciplinary record which has seen four players sent off in the past five games.
Gaetano Berardi was the latest to be shown a red card, dismissed in the first half against Cardiff and for the second time this season.
United are already in the process of securing a replacement and plan to have Christiansen’s successor in position ahead of this weekend’s Yorkshire derby at Sheffield United.
Former England manager Steve McClaren, who has been out of management since leaving Derby County last March, was pictured in the directors box at Elland Road on Saturday.
Jaap Stam, who made United’s shortlist of candidates for the job after Garry Monk resigned as head coach last summer, is rumoured to be set to leave Reading in the days ahead with his side struggling in the bottom half of the Championship.
Former Leeds boss Simon Grayson, meanwhile, is believed to be keen on the post having left Sunderland in November and recently turned down a job at MK Dons. Grayson managed United between 2008 and 2012 and won promotion from League One in 2010.
A statement from Leeds issued on Sunday night read: “Leeds United can confirm that head coach Thomas Christiansen has left the club.
“Chairman Andrea Radrizzani and the board of directors would like to thank Thomas and his staff for their hard work over the past eight months. The club will be making no further comment at this time.”
Christiansen’s assistants, Julio Banuelos and Paul Butler, have also left Elland Road along with fitness coach Ivan Torres.
Christiansen, a former Barcelona and Hannover striker, was largely unknown when Leeds and new owner Andrea Radrizzani named him as Monk’s successor.
The 44-year-old Dane, who was capped by Spain after taking up Spanish citizenship during his playing career, had previously spent three years managing in Cyprus with AEK Larnaca and APOEL.
He won the Cypriot title with APOEL in 2017 and led the club to the last 16 of the Europa League but was released after one year in charge.
Christiansen won 15 of his 35 games as head coach at Leeds but had failed to claim a victory since United’s Boxing Day trip to Burton Albion.
His dismissal leaves the club looking for their eighth head coach in four seasons.