The 36-year-old former Sale and Saracens fly-half, capped 38 times by England, will work under Exiles director of rugby Nick Kennedy.
Hodgson amassed 2,623 points in his Premiership career before making his final appearance in May 2016.
England women and former London Welsh assistant coach Matthew Ferguson also joins the club as scrum coach.
Irish, promoted back to the Premiership in May, begin their season against Harlequins at Twickenham in the London Double Header on Saturday, 2 September.
Premiership record points scorer Charlie Hodgson has joined London Irish as kicking coach.