He joins from Toyota Motor Europe, where he was director of Lexus Europe. He has previously held the marketing director role at Toyota GB.
Harrison replaces, and reports to, Jon Williams who was promoted to managing director of Toyota GB in October.
Before joining Toyota in 2000, Harrison spent 10 years in sales and marketing roles with Ford.
Harrison says Toyota is confident it can “regain sales momentum” in a UK car market that is currently in decline.
Harrison’s appointment comes as Toyota sets a new target to increase global sales by 3% next year, focusing growth in Europe to offset sharp decline in its domestic Japanese market.
The group expects Toyota-brand vehicles’ overall overseas sales to rise 8% to 6.4 million vehicles in 2011 while it is expecting a 17% fall in sales in Japan.
Separately, the car manufacturer has been fined a record $32.4m (£20.8m) in the US, over its handling of product recalls in the past 12 months. It follows a previous fine of $16.4m, agreed in April.
Toyota issued 14 recalls in 2010 affecting more than 10 million vehicles.
Toyota recorded a 7% rise in sales in 2010 despite the product recalls.