The former Sunderland boss will replace Jim Magilton, who was saked yesterday.
The Irishman said: “I truly believe that I am joining a club that has the potential, ambition and infrastructure to once again be a Premier League side.
“The club’s owner and chief executive impressed upon me their total focus on achieving this quest at the earliest opportunity and I can’t wait to get started.”
Ipswich owner Marcus Evans is set to hand Keane £20million to spend on new players that they need to reach the Premier League.
Evans said: “I am delighted that Roy has agreed to join us and we are completely aligned in our ambitions for Ipswich Town.
“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.”
