The Spanish coach, who led the Teessiders to promotion last season, has been under severe pressure, with fans calling for his head after an woeful run of form.
The 43-year-old Spaniard departed on Thursday morning with Boro 19th in the table having not won in 10 league outings since December 17, and scoring only three goals in the process.
And in a statement on the club’s official website on Thursday, Middlesbrough confirmed they had parted company with Karanka.
The statement read: “Middlesbrough Football Club can today confirm the departure of Head Coach Aitor Karanka. Following discussions, both parties have agreed that it is in the best interests of the club to make this change.
“The club would like to thank Aitor for all his hard work over the past three-and-a-half years and for the success we’ve had during that time. We wish him all the best for the future.”
Karanka had remained confident of easing promoted Boro back above the safety line in the remaining 11 games of the season and was encouraged by his team’s display in Saturday’s 2-0 FA Cup quarter-final defeat by Manchester City.
However, he did not get the chance as his reign came to an end after three years and four months.
Karanka said: “I’d like to thank Middlesbrough for a wonderful opportunity and the players, staff and all the people at the club who I have worked with. I’d also like to thank the fans for their support.
“This club will always hold a special place for me and I wish everyone connected with Middlesbrough Football Club the very best for the future.”
Assistant head coach Steve Agnew will take over first-team duties with immediate effect, and that will mean preparing the team for Sunday’s league clash with Manchester United, managed by Karanka’s mentor Jose Mourinho with whom he worked at Real Madrid.
Next Middlesbrough manager betting
Agnew currently heads the betting for the vacancy with bookmakers William Hills, with Steve McClaren and Roy Hodgson also in contention.
Next permanent Middlesbrough manager: 5/4 Steve Agnew; 6/1 Steve McClaren; 8/1 Roy Hodgson; 10/1 Nigel Pearson; 10/1 Alan Pardew; 10/1 Jurgen Klinsman; 14/1 Roberto Di Matteo; 14/1 Jaap Stam; 16/1 Alex Neil; 16/1 Martin O’Neil; 20/1 BAR
Karanka time in charge littered with disappointments
Despite chairman Steve Gibson’s well-known loyalty to his managers, it seemed only a matter of time before a change was made.
Karanka arrived on Teesside in November 2013 with the club languishing in the lower reaches of the Sky Bet Championship table, and swiftly turned things around.
They narrowly missed out on promotion at the end of the 2014/15 campaign, when they were beaten by Norwich in the play-off final at Wembley, but won their return to the big time automatically after an eight-year absence 12 months later when they finished as runners-up to Burnley.
Life in the top flight started positively with five points from the first three games, which included a derby victory at Sunderland, and, although Boro initially proved difficult to beat – they managed draws at both Arsenal and Manchester City – the goals, and as a result points, started to dry up.
Their last league win came at home to Swansea on December 17 and, although an extended FA Cup run gave the fans something to cheer, Karanka’s reign was unravelling amid a feeling that Plan A was not working and there was no Plan B.
Having briefly been banished from the club last season after a training-ground disagreement with some of his players, the Spaniard criticised supporters and the club’s January recruitment process, when targets such as Robert Snodgrass, Bojan Krkic and Jese Rodriguez failed to arrive.
In recent weeks, Gaston Ramirez, who attempted to engineer a move to Leicester during the winter transfer window, and Alvaro Negredo have found themselves sitting on the substitutes’ bench, while Stewart Downing and Patrick Bamford have not even made the matchday squad with Karanka pointedly claiming he needed “18 fighters”.
His departure may come as a relief to some of those men, but the club remain in a parlous position with time fast running out.