Lam leaves Connacht for Bristol
Lam led Connacht to their first Celtic League title earlier this year and replaces former England and Scotland coach Robinson, who was axed as Bristol's director of rugby in November after a winless start in the Premiership.
The 48-year-old's first major challenge could be trying to guide Bristol back to the Premiership as they are favourites for relegation this season having lost all 10 top-flight matches so far this season.
Lam has already insisted he will still join Bristol even if his new club have dropped down to the Championship by the time he arrives. Mark Tainton will remain in his role of acting head coach for the remainder of the season.
"I'm committed to Bristol irrespective as to what happens in the short term. Everything is in place for the club to be a force in the future and I'm honoured to be invited to join the journey.
"I'm excited about the opportunity to coach and lead Bristol Rugby – a proud club with history, tradition and a bright future ahead.
"As with my decision to help Connacht four years ago, my coaching philosophy is very much aligned to assisting them in making Bristol a club where the Bristol community can be inspired and Bristol players have a genuine pathway to represent England.
"This has been one of the most difficult decisions I've had to make in my life as Connacht and Galway is such a special place for myself and my family," Lam said.
Agence France-Presse
