Byrne fills the void left by Willie Anderson who left Leinster to join up with Matt Williams with the Scotland squad.
Byrne was scheduled to lead the Ireland Schools squad to Australia later this month but will step down to join a revamped Leinster set-up.
The Dublin born coach has been a teacher at Gonzaga College in Dublin and also coached All-Ireland League clubs Terenure and UCD.
He has experience of working with many of the current Leinster squad during their school years, and his background of coaching young players was seen as valuable by Leinster Lions management as the Loins look for continuity ahead of a tough season.
Leinster are pooled with Bath Rugby, Benetton Treviso and Bourgoin in the Heineken Cup, and will embark on a Celtic League and Cup campaign that spans September to May.
Leinster had a disappointing season last year, failing to make the quarter-final stages of the Heineken Cup and finishing in eighth spot in the Celtic League.