Delaney, who takes up his post with immediate effect, will join the Exiles from Championship club Nottingham, where he spent seven years as rugby director.
Former Irish coaches Toby Booth and Neal Hatley recently left the Aviva Premiership outfit to take up posts at Bath.
Delaney had three seasons with Irish as a player, featuring in the second-row, before being appointed Nottingham's rugby director for the 2005-06 campaign.
"It is great to be returning to London Irish," he said.
"I enjoyed plenty of good times with Irish as a player, and I am sure I will experience the same as a coach."