Tierney has been undergoing medical treatment following a cancer diagnosis but began a phased return in November, with chair Richard Collier-Keywood and the rest of the Union’s executive stepping in on an interim basis.
Collier-Keywood will now revert to his responsibilities as the WRU’s chair in January.
“This is a pivotal time for the game in Wales and, whilst I’ve been constantly kept informed and am across all developments, I’m looking forward to being able to contribute directly again,” said Tierney.
“My treatment is going well and I’ve received a positive prognosis which allows me to return in the New Year.
“I’d like to thank everyone who has wished me well over my time away and sent positive messages of support.
“The Welsh rugby family has been incredibly supportive and I feel blessed to be a part of it.
“Of course, there are significant and major challenges presented to Welsh rugby at this time but there is also a huge opportunity for us to forge a way ahead in our professional game which will safeguard its future.
“There is a lot more hard work ahead, but our strength in Welsh rugby is in our ability to unite and work together towards one collective aim and I am looking forward to contributing to this again.”
READ MORE: WRU CEO Abi Tierney to Step Away for Cancer Treatment
Collier-Keywood said: “I know I speak on behalf of the whole game in Wales when I welcome Abi back into her role.
“We are making progress in our transformation programme for the professional game in Wales, but I know Abi’s return will add new and positive impetus at this pivotal time.”
READ MORE: New WRU Chief Abi Tierney Insists She’s Done Her Homework And Knows What She Is Joining
