The law firm, which has offices in Leeds and Sheffield, has established Iris, an LGBT network that is open to all of the firm’s employees.
The international group is led by co-chairs Milena Falciano and DeanPeachey, who are both lawyers from DLA Piper’s Leeds office.
Ms Falciano said: “People should not be judged on who they are attracted to or which sex they identify with, but instead on their personal merit.
“I think having a female straight ally and a gay man leading the group together really shows that sexual orientation is not a barrier at DLA Piper.
“As one of the world’s largest global law firms we are intrinsically diverse and I truly believe that it is our differences and acceptance that make us such a strong global team.”
The launch will take place at an evening event at DLA Piper’s London office, hosted by global co-chairman, Juan Picon, The event will include a speech from Mr Thomas, the former Welsh rugby player.
In August 2010, Mr Thomas came top of the Pink List for the 101 Most Influential Gay People in the UK.
During his speech, Mr Thomas will speak about his sporting career, as well as his personal life, and the difficulties he experienced when trying to come to terms with his sexuality.
The group was named following a global internal competition, which was led by Ms Falciano and Mr Peachey. In Greek mythology, Iris is the personification of the rainbow and also the messenger of the gods, who links them to the mortals.