During his seven years at the company, Coltart has steered BAE's press office through a series of controversies. Last year it was alleged that BAE used a £60m slush fund to oil the wheels of the Al
Yamamah deal to sell arms to Saudi Arabia.
BAE, which denies the allegations, continues to co-operate with the Serious Fraud Office's investigation.
A recruitment process is under way to find Coltart's successor.