The recruitment adds to the Welsh contingent in the Lions' backroom team and Jenkins will link up with the side when they meet in May.
The WRU Group Chief Executive, Roger Lewis, said: "The appointment of Neil is yet more confirmation that we have assembled a remarkably skilled backroom and coaching team here in Wales.
"The complement of coaches, analysts and conditioners from Wales is testimony to the strength of our systems and structures which are supported by incredibly talented and experienced individuals.
"We now have Warren, Rob and Neil along with our analysts Rhys Long and Rhodri Bown plus Prabhat Mathema our medical performance manager and Adam Beard all travelling to Australia with the squad.
"We have worked hard here in Wales to create the right environment and recruit coaching and backroom staff with the calibre to make sure we coach winning teams.
"This has been a clear priority and we are now making our vision a reality when the Lions show such confidence in the staff from Wales.
"I am delighted for all the individuals who will be travelling with the Lions and I am confident they will also be accompanied by a strong contingent of Welsh players on the tour.
"The strength of the coaching and backroom team we are sending to Japan under the leadership of Robin McBryde also proves what depth of quality we now have in our backroom team."
Jenkins will now not travel to Japan with Wales this summer but the side will benefit from this experience on his return according to McBryde, who will lead Wales on the two-test tour.
"It's a great opportunity for Neil and I'm delighted for him," said McBryde.
"Neil excels in his field and it's a chance for him to show that once again with the Lions. From a Wales point of view it will add to his coaching experience and CV and I'm sure we will reap the rewards on his return."
Speaking on his appointment, Jenkins, who is Wales' record points scorer, said: "It is a great honour to once again be part of a British and Irish Lions tour. I am delighted and grateful to have been offered this opportunity to join the 2013 coaching staff.
"As a player, I was lucky enough to tour Australia with the Lions in 2001. It is a great country and they are one of the top teams in world rugby. Like 1997, it was a terrific series but unfortunately, we lost 2-1.
"I have clear ideas of what I would like to contribute and I cannot wait to get out onto the training pitch and get started."