The 98-times capped Blues flanker last played at the Millennium Stadium in Wales' 25-37 loss to New Zealand last November and is looking forward to running out again at the home of Welsh rugby.
"It will be great to be back at the Millennium Stadium. It's been a while since I've played there now and I'll get to play against a lot of my friends which will be exciting."
Wales head coach Warren Gatland has confirmed Williams' inclusion in the Baa-Baas side does not rule him out of contention for a potential return to the fold in time for the Rugby World Cup in September.
He said: "Playing for the Barbarians does not exclude Martyn from the opportunity of still being selected for our world cup squad.
"With Martyn in the opposition line-up, it's a great chance for us to see how our young back row will cope in an international match against such an experienced and world class player."
Williams added, "Hopefully, if I can put in a good performance, I can get back into Warren's plans for the world cup. Having spoken to Warren, I know it's a case of the more Welsh players on the field the better. The coaches know what I can and can't do, but it will be a fantastic occasion and I can't wait to run out at the Millennium Stadium against boys I've played with there so many times.
"I would love to go New Zealand, the Rugby World Cup is the pinnacle of anyone's international career, along with the British Lions. If I was asked to go, I would grab the opportunity with both hands but there is a lot of rugby to be played before then with the end of the Magners League and the summer internationals. And the one place we have a lot of strength in depth is in the back row.
"I will just keep going for the Blues and see what happens."
Williams has a lot of history with and against the Barbarians having won his first cap against them in 1996. He has since played for them on five occasions, including a man of the match performance in their 22-5 win over South Africa in December 2007.
He said, "Having had my first cap against the Baa-Baas, the team is very important to me, and I've come full circle now to be playing for them against Wales.
"Whoever plays in the back row for Wales, it will be tough, we have some great youngsters coming through. But the Baa-Baas side will also be full of world class players - hopefully I'll be lining up in the back row alongside Sergio Parisse and George Smith which would be fantastic. There are others too - Carl Hayman is one of best tight heads in the world so we should have a great squad capable of giving Wales a stern test before the world cup."
Williams joins a list of stars already named by the Barbarians for their summer tour which includes Italian captain Sergio Parisse, France centre Mathieu Bastareaud, England's Paul Sackey and Ian Balshaw, South African duo Ruan Pienaar and Francois Steyn and props John Hayes of Munster and Ireland and All Blacks legend Carl Hayman.
Wales have lined up against the famous black and white hoops on six occasions losing four times and winning just twice - in Williams' debut in 1996 and in the last outing in 2004.
The other capped international against the Barbarians was Wales' first in 1990, which the Baa-baas won 31-24.
Tickets remaining for Wales v The Barbarians on Saturday 4 June at the Millennium Stadium (2.30pm) are priced at £40 and £30 for adults, £100 for a family ticket (2 adults 2 children) with a new category introduced this season of £15 for the under 18s enclosure.
Tickets can be purchased online at www.wru.co.uk/tickets, by calling the ticket hotlines 08442 777 888 or 02920 230130, and to personal callers at the Cardiff Arms Cafe / Store, 8 Westgate Street, Cardiff and Ticketline, 47 Westgate Street, Cardiff.
Wales' record v Barbarians:
Wales 10-26 Barbarians 31 Cardiff Arms Park 17-04-1915 L
Wales 24-31 Barbarians, Cardiff Arms Park, 06-10-90 L CAPPED
Wales 31-10 Barbarians, Cardiff Arms Park, 24-08-96 W CAPPED
Wales 38-40 Barbarians, Millennium Stadium, Cardiff, 20-05-01 L
Wales 25-40 Barbarians, Millennium Stadium, Cardiff, 29-05-02 L
Wales 35-48 Barbarians, Millennium Stadium, Cardiff, 31-05-03 L
Wales 42-0 Barbarians, Millennium Stadium, Cardiff, 26-05-04 W