At the same time as news broke that Leeds were close to appointing a new boss, former Borussia Dortmund man Thomas Tuchel ruled himself out of the running for the Southampton job.
United finalised a deal with Christiansen on Wednesday as he agreed to replace Garry Monk who resigned three weeks ago.
'We are delighted to make this announcement as it successfully concludes what has been a thorough and extensive search, following a huge level of interest from all over the football world, ' said Leeds managing director Angus Kinnear.
But APOEL chose not to renew Christiansen's 12-month contract and released the 44-year-old in the wake of a defeat to Apollon Limassol in the national cup final.
With Monk leaving early this summer, and Kyle Bartley - Jansson's partner in central defence last season - looking unlikely to return to Elland Road, the pending arrival of Jansson will be a major positive for Leeds.
Christiansen was not featured on the long list of candidates linked with the Elland Road job, with the likes of Jaap Stam, Aitor Karanka, Fernando Hierro, Alan Pardew and Victor Sanchez featuring among the bookmakers' favourites.
A striker in his playing days, Christiansen turned out for Barcelona's B team and also had spells with Spanish clubs Sporting Gijon, Osasuna, Racing Santander, Oviedo and Villarreal.
His best season came in the Bundesliga with Bochum when he was joint-top scorer with 21 goals in 2003.
As usual, Leeds United fans have taken to Twitter to react to the appointment.
His only previous managerial experience comes in the Cypriot league, as he managed AEK Larnaca between 2014 and 2016, before taking charge at Apoel Nicosia last season.