Greenstock (29) has made four appearances for England at centre, scoring two tries. He joins the Exiles from NEC Harlequins where he has been since the 1999/2000 season having previously played for London Wasps.
Announcing Nick's signing, Conor O'Shea, the Managing Director of London Irish said: "We realised the need to augment our resources in the midfield and also recognise that a senior player within the squad is an essential ingredient. In this respect Nick Greenstock brings talent and experience which will be vital to the squad. We are delighted to welcome him to London Irish"
Commenting on his move to join the Exiles, Nick Greenstock said "I am excited about the potential the London Irish squad represents, and have been impressed with the plans that Conor, Gary and Paul have for the club. The move represents a new challenge for me, and I am looking forward to it."