Roy Keane has been appointed manager of Championship side Ipswich Town.
The 37-year-old signed a two-year contract following the dismissal of Jim Magilton on Wednesday.
Keane has been out of work since December when he resigned as Sunderland manager, having taken the club from the Championship to the Premier League.
"I truly believe I am joining a club that has the potential, ambition and infrastructure to once again be a Premier League side," said Keane.
The ex-Manchester United captain will hold a news conference at 1600 BST on Thursday.
Ambitious Ipswich owner Marcus Evans has spent £12m on new players since he took the club over in late 2007 in an attempt to reach the Premier League.
Magilton, who took over from Joe Royle in 2006, was sacked for failing to guide Ipswich to the Championship play-off places, with assistant boss John Gorman also leaving the Suffolk club.
Coach Bryan Klug has placed in charge of the first team for Saturday's game at Cardiff City while Keane acquaints himself with his new surroundings.
Keane was in charge at Sunderland for over two years
"The club's owner (Marcus Evans) and chief executive (Simon Clegg) impressed upon me their total focus on achieving this quest at the earliest opportunity and I can't wait to get started," said the ex-Manchester United midfielder.
Keane took over as Sunderland boss in August 2006 with the club languishing second from bottom in the Championship.
He made an immediate impact, guiding them to the Championship title that season, and Evans is confident he has lured the best man for the job to Portman Road.
"We are completely aligned in our ambitions for Ipswich Town," Evans told Ipswich's official website.
"He has extensive contacts in the game and is a proven winner who encourages his team to play the attractive football that Ipswich Town fans have come to expect. I believe he is the right man to take this club where we want to be - the Premier League."
Ian Dennis, Radio 5 Live's chief football reporter, said Evans had targeted Keane weeks ago and will give his new manager financial backing for a promotion push for next season.
"But just as crucial is the fact that 15 players are out of contract at the end of this campaign which will allow Keane to shape his squad straight away," said Dennis.
Former Ipswich midfielder Matt Holland, who played alongside Keane for the Republic of Ireland, believes the new boss will command instant respect in the Portman Road dressing room.
"Everyone must have huge respect for him, for what he's done as a player and manager," Holland told BBC Radio 5 Live.
"He'll have that fear factor and sometimes I think you need that.
"Roy was probably desperate to get back into management and it's a good club with huge ambition."
Ipswich chief executive Simon Clegg said Keane's appointment demonstrates the ambition of Evans, who runs a global leadership business.
"Roy has spent a little bit of time thinking about this," the former chef de mission of the British Olympic Association told BBC Radio 4's Today programme.
"It's a big appointment for him - he doesn't make the type of commitment that is necessary to join a club like Ipswich Town lightly and without believing in potential.
"I'm not going into details of how much money is available but, having made the statement of intent that we have, the owner will support both the manager and in terms of giving us the resources we need to achieve the goal of reaching the Premier League."
Sunderland boss Ricky Sbragia welcomes Keane's return to football
Keane walked away from Sunderland nearly five months ago following the arrival of majority shareholder American Ellis Short.
The Irishman made his name as a tough-tackling midfielder, playing at the highest level with Nottingham Forest, Manchester United and Celtic, as well as making 66 appearances for the Republic of Ireland.
Current Sunderland manager Ricky Sbragia, who was first-team coach under Keane at the Stadium of Light, said Ipswich was a good fit for his former boss.
"He wanted to get back into the game as quickly as possible and he's managed to achieve that," Sbragia told Radio 5 Live.
"He'll go to Ipswich and shake it around a little bit. It's nice to see him back and I think Ipswich have made a good appointment."
I'm not really interested in it, to be honest... I'd say good luck to him and well done, but I've got more important things on my mind
Alan Shearer on Keane's return to management
Asked if Keane would be a success at Portman Road, Sbragia added: "Only time will tell with that, but it's a lovely club and always known to be a well-run club.
"They always play attractive football and it's a lovely place in the country to live. I think he'll thoroughly enjoy it."
One man who is not worried whether Keane is a hit or not is former adversary Alan Shearer, now charged with steering Newcastle clear of the Premier League relegation zone.
Asked what he thought of Keane's return to management, Shearer, responded: "I'm not really interested in it, to be honest.
"I'd say good luck to him and well done, but I've got more important things on my mind."
Ipswich are said to want Keane, who commuted from his Cheshire home to Sunderland during his time in the north east, to move closer to the club.
This should not prove a problem. After leaving the Stadium of Light, Keane said: "I'm happy to move house. I'm not tied to Manchester."
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