Roger developed his underwater field craft as a competitive spear fisherman while studying for an Honours Degree from the University of Natal in South Africa. He continued to dive while working in the digital and financial services sectors, and furthered his management training at the UCT Graduate School of Business and the London Business School.

In 2007 he began working for the BBC Natural History on the Nature's Great Events series directed by Hugh Pearson, and began his apprenticeship under cameramen Didier Noirot and Doug Anderson. During this period he narrated and co-directed three documentaries with Craig and Damon Foster. The first of these "Into the Dragon's Lair", was nominated for an Emmy for best Cinematography in 2010, and the sequel, 'Touching the Dragon" was selected as one of the feature shows for National Geographic's 125th centenary year celebrations.

In 2011 Roger shot his first blue chip sequence for John Downer's "Earthflight", for producer Rob Pilley. This was followed by a long term assignment from John Downer to film bottle-nose dolphins for the "Spy in the Pod" series which aired on BBC One in 2013, and two sequences on the BBC Atlantic series for producer Ted Giffords. In 2015 and 2016 he spent 110 days filming for Silverback Films on Disneynature's "Blue", for director Keith Scholey and worked as a second unit DOP on the National Geographic "Into the Okavango" feature directed by Neil Gelinas.

in 2017 he was appointed as the underwater DOP on the National Geographic Pristine Seas Expedition to Tristan da Cunha, led by Paul Rose, working for producer Alex Verville. For Blue Planet 2, released in October 2017, Horrocks received cinematography credits on four of the six main episodes, shooting for producers Jonathan Smith, Katheryn Jeffs and Joe Steven.

His recent and current projects include contributing sequences for Hostile Planet produced by Plimsol Productions for National Geographic, DisneyNature Elephants produced by Silverback, and Our Planet produced by Silverback for Netflix.