McCullough joined Lexus as sales operations manager in 1998 and was responsible for taking the franchise into the mainstream with the development of the IS range.
The model saw Lexus sales rise five-fold, making the UK second to the USA in market size. He also oversaw the creation of a separate Lexus dealer network to deal with the new business opportunity created by the new product.
Under McCullough, Lexus picked up successive JD Power awards for customer satisfaction and reliability.
His successor will be named in the next three to four weeks but McCullough will retain responsibility for the UK operation in the interim to ensure continuity, reporting to Thierry Dombreval, senior vice-president, sales and marketing.