The chief executive Simon Clegg said the search for the next appointment was at an "advanced stage".
The Tractor Boys had lost seven of their last nine games, dropping to 19th in the table. Ian McParland has been put in caretaker charge, with his first two games against the Premier League sides Chelsea and Arsenal.
Ipswich head to Stamford Bridge in the third round of the FA Cup on Sunday, before hosting the Gunners in the first leg of their Carling Cup semi-final on Wednesday.
Keane felt his side were capable of climbing back up the table under his guidance.
"I have a genuine belief we were making progress and that the players have what it takes to turn this season around. We were preparing well for our visit to Chelsea on Sunday and then our Carling Cup semi with Arsenal. Getting to that semi proves what I know the team is capable of," he said.
"I was also working hard to build the squad during the transfer window, looking at our options to attract new players to the club. I have loved my time at Ipswich, living locally to the club with my family, and have a massive respect for the club, its staff, the fans and the community and I wish them well."
The Norwich City manager Paul Lambert has committed himself to the club after the Canaries rejected an approach from Burnley for his services.
"I want to put the speculation to bed - I've never had any intention of going elsewhere and nothing has changed. All the speculation is wide of the mark and hopefully now the rumour mill about the Burnley job can focus elsewhere and we can all move on," he said.
Swansea City have signed forward Luke Moore, 24, from West Bromwich Albion.
"Luke comes to the club at a great age to fulfill the undoubted potential that everyone knows he has," said Brendan Rodgers, the Swans manager.
"His pace, power and finishing ability will add another dimension to our game. He's also got a great hunger for the game as he hasn't quite fulfilled his potential yet.
Hull City have signed defender James Chester from Manchester United.
Chester, 21, spent the first half of the season on loan at Carlisle.
"It's the next step up from where I've been. To come to Hull is another challenge and something I'm looking forward to," he said.
The Queens Park Rangers forward Patrick Agyemang is expected to miss up to three months with a broken leg.
It came as a shock to the player, who thought he had a calf strain. Scans revealed a stress fracture.
The Leicester City defender Michael Morrison, 22, has joined the League One side Sheffield Wednesday.
"Michael has played mainly as a centre-back but also at right-back. He's a good defender, who attacks the ball well, he's aggressive and mobile and a player who has excellent all-round potential," said the Owls manager Alan Irvine.
The Foxes were expected to spend Friday trying to secure the signing of defender Kyle Naughton, 22, from Tottenham Hotspur.
He has spent the first-half of the season on loan at the Walkers Stadium, and both parties are said to be keen to make the move permanent.