Up to 60 teams from 18 countries are expected to take part and the countdown is now on for the competition, scheduled to run from 30 April to 2 May 2021.
Gareth Thomas enjoyed a career in international rugby for some 15 years, came out as gay in 2009 and as HIV positive last September.
He was quoted by Gay Star News as saying: ‘As one of the most important LGBT+ sporting events in Europe, I was honoured to get involved in last year’s Union Cup, which broke down social barriers and bridged together communities across Europe.
‘I am proud to be an ambassador for the Union Cup 2021 and breaking down barriers in LGBT+ sport.’
The cup has been running every two years since 2005, with host cities of Montpellier, Copenhagen, London, Amsterdam, Bristol, Brussels, Madrid and Dublin.
Tournament director Alistair Burford said: ‘Birmingham Bulls RFC is thrilled to be the host club for the upcoming Union Cup 2021 in Birmingham. With COVID-19 prompting the postponement of the Bingham Cup until 2022, all eyes will be on the Union Cup 2021.
‘Bringing the Cup to Birmingham has been a dream of the Bulls for many years. Birmingham is the UK’s second city and we’re looking to giving our visiting teams and fans a first-class experience.’
The club is promising an inclusive tournament for all, ‘irrespective of creed, colour, sexuality, gender or even if they’ve been to a rugby match before’.