Dr Brian Lang, who held the same role as former Royal Bank of Scotland chief executive Sir Fred Goodwin, has stepped down from the company after just 18 months in the job.
The former St Andrews University principal said he had made the decision to leave the embattled firm after finding his workload there had slowed.
Hit hard by the recession, the company has lost a series of senior figures in recent months and cut more than 150 jobs worldwide since last year. Dr Lang insisted the decision to leave had been entirely his own, adding that he was "still on hand" to do some project work for RMJM, whose buildings include the Scottish Parliament, the Falkirk Wheel and the planned Gazprom Tower in St Petersburg, Russia.
"There's just not that much business around at the moment," he said. "I wanted to free up my diary for other things. It was very much my decision."
In addition to his work with RMJM, Dr Lang, who held the top position at St Andrews University from 2001 to 2008, has been working as an independent educational consultant.
It has been claimed that Sir Fred, who was appointed to RMJM last January, has taken an increasingly prominent role at the firm.
Some sources have claimed he is essentially "financial controller" at the company, which has been accused of late payments to its staff in various offices worldwide.
"As far as I'm concerned, he's doing a great job," said Dr Lang. "He was brought in to take a look at the business and he has carried out that job very well, in my opinion."
A spokesman for RMJM, which was earlier this year named the fifth largest international practice and is run by Peter Morrison, said Dr Lang had departed after a specific project came to an end.
"We can confirm that Brian left as an advisor a few months ago, having completed an education-related project. We are grateful for his contribution and look forward to working with him again in the near future."
The RMJM post was not the first time Dr Lang had had a professional link to Sir Fred, who was hired at RMJM on a rumoured six-figure salary following a long friendship with chairman Sir Fraser Morrison.
Just months before the banking crash and the chief executive's dramatic departure from RBS, Dr Lang had been lined up to take over as dean of a new business school planned for the Gogarburn campus. But the role was immediately scrapped by Stephen Hester, the incoming chief executive.Dr Lang was hired by RMJM - which also boasts Russian economist Dr Vladimir Kvint as a special advisor - just months later.
RMJM, which has admitted cash flow problems as the result of the economic downturn, last year axed dozens of jobs at its Scottish operations and asked staff to take a 10 per cent pay cut due to a slowdown in business.
Last month, it emerged that Stirling Prize winner Will Alsop, who was last October tasked with heading up the firm's rapidly expanding London office, had failed to bring in a single design project for the business.
Earlier this year, RMJM accounts showed that pre-tax profits in the year to 30 April 2009 fell to 5.7 million from 7.9 million in 2008.