Thomson, who has been with the firm for the last 20 years, is now the majority shareholder and becomes chairman and managing director, while Wyrley-Birch, who joined 12 years ago as a trainee, becomes a director.
McCoull, whose father Fin had owned the business before him, will remain involved with the company as head of country house valuations.
Speaking to ATG, Thomson said he was proud to become owner of the oldest auction house in the North East (dating back to 1840) and one of longest established firms of any type in Newcastle itself.
However, he stressed that despite “the change at the top, it’s very much business as usual” and the firm’s auction calendar remains unchanged.
Newcastle-born and bred, Thomson first worked at A&G as a summer job when he was 16.
He continued to work there during vacations while he completed a degree in fine art valuation at Southampton Solent University, before joining the firm full-time in early 1990s.
Thomson had a five-year spell as a valuer at Bonhams Knightsbridge from 1992-97, after which he returned to the North East to run A&G’s silver and jewellery department.