Martin O'Neill was hired as Ireland coach on Tuesday and will have former Manchester United captain as his assistant in a box-office pairing tasked with reviving the team's fortunes.
The 61-year-old O'Neill returned to management eight months after the Northern Irishman was fired by Premier League club Sunderland, while Keane has been a TV pundit since leaving as Ipswich manager in 2011.
Keane's appointment is a surprise, as the outspoken former midfielder has had a volatile relationship with the Football Association of Ireland and walked out of the 2002 World Cup without kicking a ball.
"Today, the FAI board is appointing two Irish legends as manager and assistant manager of our national team," FAI chief executive John Delaney said.
Ireland has taken its time appointing the successor to Giovanni Trapattoni, the veteran Italian coach who left in September. It settled on two of the biggest names in Irish football.
"I'm the bad cop and he's the bad, bad cop," O'Neill told British broadcaster ITV. "We're excited by it and I'm looking forward to it greatly."
O'Neill's first matches in charge will be friendlies against Latvia at home on Nov. 15 and Poland away on Nov 19. Ireland failed to qualify for next year's World Cup finals in Brazil.