Simmons's contract will be for a period of just over two years, up to the conclusion of the 2009 ICC Trophy, which is being held in the UAE in April of that year.
"I am very pleased to be joining the Irish Cricket Union and look forward to working with both players and administration. I'm sure I will able to continue the progress that Irish cricket has made over the past few years," said Simmons.
The former West Indies international played in 26 Test matches and 143 One Day Internationals, and was coach of the Zimbabwe team in 2004-5.
Birrell, who has guided Ireland to their first ever appearance at the World Cup which starts next month, will step down after the Caribbean tournament.