The match has been organised to commemorate the 130th anniversary of the formation of the WRU as the governing body of the union game in Wales.
Wales coach Warren Gatland will be out to rewrite the history books which show that Wales have only beaten the Barbarians twice and have lost five times.
Caps have been awarded by Wales twice before in games against the Barbarians first in the Baa Baa's centenary celebration match in 1990 and again in 1996.
The first Wales versus Barbarians game took place in 1915 when Wales lost by 26 points to 10 and the last encounter between the two teams was in 2004 when Wales secured their second victory by a margin of 42 - 0.
The last capped international against the Barbarians in 1996 featured Rob Howley and Neil Jenkins, both currently integral parts of the Wales national squad coaching team, as half backs for their country
The match also marked the first cap won by Martyn Williams who has currently played 98 times for Wales.
On June 4 the Barbarians will bring a formidable side to the Millennium Stadium under a coaching team which will be officially announced shortly.
The Barbarians have already begun their match planning and are also seeking to name a captain soon for the match.
To mark the 130thanniversary the WRU is inviting a 1,000 voice massed choir to sing at the stadium before and during the game to help create a unique match-day atmosphere for fans.
The Chairman of the WRU, David Pickering, said: "We are delighted to announce that Wales will award full caps for this important and historic fixture.
"The game represents the continuation of a proud history of encounters which have featured some amazing rugby down the years.
"Every player selected to pull on the Welsh jersey on June 4 will be fully aware there is a lot at stake in the fixture."
The Group Chief Executive of the WRU, Roger Lewis, said: "Warren Gatland will be out to prove his team can overturn a tough history of losses against the Barbarians and deliver a win for the record books.
"He and his coaching team will also be closing in on deciding the make-up of their Rugby World Cup squad so the players will want to impress.
"Barbarian fixtures are always built around exciting rugby so it will be a chance for Wales to fine tune some strategies and show just how good we are.
"Match-day will be extra special because the WRU will be celebrating our 130thanniversary which is a vitally important milestone in our history.
"From that first meeting in Neath on March the 12th1881 rugby has grown into the national sport of Wales and our nation is known around the world for our prowess in the game.
"Many of the greatest Welsh players have worn the Barbarian jersey and Penarth has been renowned as the spiritual home of the team which has no country or clubhouse.
"I know Welsh fans will want to be at the Millennium Stadium to ensure the Welsh boys know they will go forward into the Rugby World Cup with their full support.
"It is a mouth-watering prospect and we have reflected its importance by introducing a ticket pricing structure which will ensure that fans and families will be able to get involved and be there."
Barbarians' president Micky Steele- Bodger said: "It is a great pleasure for the Barbarians to be invited to share in this significant match.
"As a club we are very proud of our own history and, in particular, we are conscious of the contribution of so many Welsh players and administrators to our cause over the years.
"Returning to the Millennium Stadium on 4 June is the perfect opportunity for us to return the compliment."
Wales head coach Warren Gatland added:"The first thing for the squad players to do is impress us physically and in rugby terms on the training camps, then the opportunity comes against the Barbarians.
"They are always an unknown quantity and we won't really know what to expect from them until that first whistle goes, but that is the attraction of Baa Baas rugby.
"I am delighted at the schedule of warm up fixtures we will be playing in June and August next year it is important for us to measure our progress against some top class opposition.
"The Welsh support is very important to us as a squad and I am extremely pleased the WRU has devised this excellent ticket policy to encourage as many fans as possible to watch the games.
"It is going to be an exciting and challenging campaign in New Zealand and these games will give the boys the sort of send off they need before taking their hopes and aspirations into the Rugby World Cup arena.
"The Millennium Stadium is a fantastic venue and games against the Barbarians, England and Argentina will give us the best possible chance to fine tune our rugby.
"These matches will be our final games on home soil, the last chance for the players to impress before RWC selection, which must be completed 48 hours after we face the Pumas, and our final chance as coaches to make some tough decisions.
"It's also the last chance for the fans to show their support and give a final send-off before we travel to the other side of the world to represent Wales at the biggest tournament in rugby."
Tickets remaining for the summer RWC warm-up fixtures against the Barbarians and England at the Millennium Stadium are priced at £40 and £30 for adults, £100 for a family ticket (2 adults 2 children) for the Baa Baas game and £110 family ticket for the England match, with a new category introduced this season of £15 for the under 18s enclosure.
The final game on homes soil against Argentina is priced at £30 and £20 for adults, £70 for a family of four and £15 for the under 18s enclosure.
Tickets can be purchased online at www.wru.co.uk/tickets or by calling the ticket hotline 08442 777 888.
Sat 4 June 2011 - Wales v Barbarians, Millennium Stadium (KO tba)
Sat 13 Aug 2011 - Wales v England, Millennium Stadium (KO 2.30pm)
Sat 20 Aug 2011 - Wales v Argentina, Millennium Stadium (KO tba)