Mr Johnson has stepped down from his position after four years at the company and he will now be replaced by chairman Stef Stefanou.
Mr Stefanou previously held the chief executive role before Mr Johnson’s appointment in 2005.
The news of the change comes as a surprise with Mr Johnson admitting he does not know what he will do next.
He told Construction News: “I have no firm plans about what I will be doing after the end of the month.”
In an email to staff this week, Mr Stefanou said: “Rob was appointed as chief executive three years ago to lead an expansion of the business in scale and scope.
“However, the prevailing and projected market conditions mean that this can no longer be the case and we are taking a number of measures to enable us better to face the challenge of the present economic climate.”
Mr Johnson, 50, joined Doyle from support services firm Jarvis, where he was commercial director.