Chairman Gareth Cooper said the firm was also looking to strengthen the board by appointing a commercial manager, who would also look at future acquisitions.
Cooper said: "John has been with the group for more than 13 years and has worked closely worth Richard over that period. John's appointment will ensure continuity of policy and direction."
The management changes came as WYG announced that turnover had risen 20% to £76.6m and profit had risen 14% to £5m for the year to 30 June.
The firm pointed to six long-term framework contracts struck in the last year as evidence that growth would continue.
The firm is a principal support provider for Defence Estates, the Ministry of Defence's property arm. This has contributed £136m to the group's future order book.
Cooper said the firm was on the look out for acquisitions.
He said: "Few acquisition opportunities arose during the second half of the year but interesting situations are now emerging."