Mathew James, from Trehafod, Rhondda Cynon Taff, was shot three times as he protected his fiancee in the resort of Sousse in 2015.
He was given the award on Saturday.
BBC Wales broadcaster Roy Noble was made a Knight of the Order of St John at the ceremony, an honour conferred by the Queen.
Keith Dunn, chief executive of St John Wales, said: "This is an extremely rare and prestigious award and we are delighted to be able to honour Mr James's presence of mind and control under great pressure."
Mr James's partner, a St John Wales member as a child, added: "I'm so proud of Mathew and would like to thank everyone at St John Wales for recognising his bravery."
Thirty Britons, including one from Wales, were killed in the attacks at Sousse in June 2015.
The annual service at Llandaff Cathedral recognises long-serving St John members and outstanding achievements from volunteers and members of the public.
Radio and TV presenter Mr Noble was presented with his insignia as a knight by the Prior for Wales, Dan Clayton Jones.
It recognises his long association with the charity as a former trustee and as current ambassador for the Welsh first aid charity.
The Order of St John dates back to the time of the Crusades. It began with a number of individuals who were involved in the founding of a hospital in Jerusalem.
Knight is the second highest honour within the organisation.
A holidaymaker who became a human shield during the Tunisia beach attacks has been presented with a life saving medal by St John Wales.