Originally a swimmer Harrison joined the world of Triathlon aged 10. In his younger years, Harrison won two South East Regional Triathlon Series titles and a Schools Regional Road Time Trial Championships in cycling. 

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From the age of 15, Harrison raced the National Elite Super Series of short course triathlon with further experience on ETU European Junior Elite Cups circuit. 

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At the end of 2018, Harrison turned his focus to Olympic and 70.3 (half Ironman) where his goals now lay.