The 36-year-old had been working in a CEO role for the Cornish Pirates, but it has now been announced that he will be moving to the WRU at the end of September.
Lewsey told Wales Online: "I am delighted to have been offered this opportunity to play a pivotal role in ensuring the strength and wellbeing of the national sport of Wales.
"Everyone involved in rugby knows how passionate the whole of Wales is about the sport so I am fully aware of the huge responsibility that I am accepting.
"This a challenge and an opportunity that I am determined to cease with total commitment and I promise everyone in Wales that I will give my all to the task ahead."
The former England player won the World Cup in Australia in 2003.