Deacon, 34, retired from playing at the end of the 2011 season having made four appearances for England and 10 for Great Britain, before moving in to coaching at his hometown club.
McNamara said: “Paul is one of the best upcoming coaches in the country with a wealth of experience playing at the top level in the Super League. As a player, Paul was a model professional and he is now developing into an excellent coach. I’m sure all the players involved in the England programme will benefit from his vast knowledge.
“He will be able to offer understanding and experience in a number of areas and his insight as a top class half-back will be invaluable in the work he will be doing with the playmakers in the squad. I would like to place on record my thanks to Wigan Warriors and to Chairman Ian Lenagan and Head Coach Shaun Wane for supporting this appointment.”
Deacon told the Warriors’ official website: “It is a great honour and a terrific opportunity for me and one I’m really looking forward to being involved with.
“I am looking forward to working with the best English players and passing on my experience. We have some fantastic talent coming through and to be involved at the highest level enabling England to realise its goal of winning a major tournament is something I will relish.”
Deacon spent much of his playing career at Bradford, scoring more than 2500 points in 324 appearances.
He started his career at Oldham, and went on to win five Super League titles, four with the Bulls and one with Wigan.
The half-back also won the Harry Sunderland Trophy for Man of the Match in the 2002 Grand Final, which Bradford lost 19-18 to St Helens.