The South African-born former England utility back will work alongside head coach Stuart Lancaster, forwards coach Graham Rowntree and backs coach Andy Farrell.
Catt, 40, impressed Lancaster with his work during England's tour of South Africa this year.
"Mike made a big impression in South Africa, both on the players and the management," said Lancaster.
"When we got back I asked him to outline his vision for developing not only the skills of the senior team, especially in attack, but with our younger players in the Saxons.
"Having played at the highest level for many years and developed his coaching during his time at London Irish he has a clear plan for developing these skills."
Catt, who won 75 caps, played in every backline position for England except scrum-half and was a member of their World Cup-winning squad in 2003. He retired in 2007.
"I loved working with the squad in South Africa and, while gutted not to win the series, I can see that this group of players is heading in the right direction," Catt said.
"Stuart, Graham and Andy did a fantastic job in the Six Nations and to be able to work with them and the best players in England is a great honour."
- Stuart Lancaster
- Graham Rowntree
- South Africa