Pendred was educated in Belvedere College, Dublin and won a Leinster Senior Cup medal in 2005 alongside Future Irish international Cian Healy.

Pendred started his professional career in 2009. He became the number one ranked welterweight in Ireland during 2010 after winning the national title. In March 2013 he became the Cage Warriors Welterweight Champion after beating the title holder Gael Grimaud in London, England.

Pendred attended Dublin City University where he studied forensics, he graduated with a BSc degree in Analytical Science in 2012.

Cathal was the subject of a 2013 MTV UK mini-documentary entitled "Pendred".

In April 2014 Cathal was pictured carrying a baby dolphin into the ocean. The dolphin had become beached and was unable to return to deep enough water on its own. A picture was taken with the dolphin in Cathal's arms as he carried it into the sea, this picture went viral soon after the incident. Subsequently the story was reported across the globe.

In 2015 Pendred became the first UFC fighter to support an anti-domestic violence group. He spearheaded a campaign which promoted the positive influence men can play in stopping domestic abuse of women and children. The campaign involved the release of a powerful youtube video in which Pendred spoke about the role men can play in preventing abuse.

On May 23rd 2017, it was announced that Pendred had been cast in a lead role in the Amazon produced TV series Lore, which is based on the popular podcast of the same name. Pendred will play Michael Cleary, a real-life character from Irish folklore in the horror anthology series. Michael is married to the younger Bridget (played by Holland Roden). When Bridget starts making more money than he does, and starts questioning his decisions, Michael is convinced that his loving wife has been replaced by a changeling. Lore premiered on October 13, 2017.