Thomas, who scored the vital winning try for Wales in their dramatic 19-12 World Cup final win over Argentina in Dubai earlier this year, is due to play for the London Welsh-based Voyageurs team.
They are one of a number of invitation teams who have been brought in to give the Diamond Jubilee celebrations an extra gleam at the Cwrt-y-Vil home of Old Penarthians in Penarth.
Thomas could run into a familiar face in former Wales Sevens skipper Jonathan Edwards, who has been named in the South Wales Fire Service squad. The Scarlets back row forward missed the World Cup triumph because of injury but has proved himself to be an inspirational leader for Wales on the IRB World Series circuit down the years.
The Young Ospreys were the winners of last year's competition and they will be back among the 16 teams trying to pick up the award once again. This year, though, they will have regional rivalry from a Cardiff 'Baby Blues' squad who are entering for the first time.
Of the original invitees to the tournament, only five remain in this year's draw. The hosts, Old Penarthians, Cardiff HSOB, Old Illtydians, Old Cantonians and Cowbridge GSOB. Of these, only Old Penarthians and Old Cantonians have been ever present.
The tournament was the 'brain child' of the then Old Pens secretary, Bill Whittaker, and the third weekend in May has been the traditional date for a tournament that has been graced by many of Welsh rugby's greatest sevens exponents down the years.
David Bishop was twice a winner of the Player of the Tournament award playing for Old Illtydians and the Phillips brothers, Andrew, David and Paul all picked up the individual award playing with Caerphilly GSOB.
Another member of Wales' World Cup winning side in Dubai, Rhodri McAtee, was the star turn in 2003, while Mark Ring put on a show for the crowd within hours of returning from a tour of South Africa with Cardiff.
The tournament kicked-off at the Penarth County School, which remained its home until 1963. In 1964, the sevens became the first function to be held at the newly completed clubhouse in St Marks Road.
Fittingly, the first winners were Old Penarthians, although the most successful side in the tournament has been Caerphilly GSOB, with nine victories from thirteen finals.
Among the guests of honour at the birthday event will be one of the members of the original Old Penarthians team that won in 1950, John Ratcliffe, while the long serving secretary, and now club President, Roy Churchill, who has been master of ceremonies at the past 42 events, will also be on duty again.
The 16 invited teams for the 60th Old Penarthians Sevens are: Ysgol Glan Taf OB, Cowbridge GSOB, Voyageurs, South Wales Fire Service, Old Penarthians, Old Cantonians, Legionnaires, Old Breconians, Cardiff 'Baby' Blues, Pontyclun CSOB, Old Illtydians, St Josephs OB, Young Ospreys, Cardiff HSOB, Warriors, Cardiff & District.