Sir Ron (73) had earlier signalled that he would stand down as chairman, but he remained on the board as a non-executive director.
Craigs Investment Partners broker Chris Timms said it was a sad exit point for Sir Ron.
"He will be disappointed with the share price over the last two years with the stock languishing as it has done. He has been working hard on all the issues in front of GPG to wind up the company, but it hasn't happened."
The shares, which peaked in the middle of 2006 at $1.80, last traded at 70c, having fallen 8.3% this year.
The investment in Coates had proved difficult and having GPG wound up and paid out in tough economic circumstances had proven harder than expected, Mr Timms said.
Mr Johnson becomes chairman two and a-half months after investors forced the board to back down from carving up the business and dividing up the money.
Mr Johnson was one of four independent directors brought in to help develop a new strategy for the ailing investment company.
Sir Ron said in a statement he was delighted Mr Johnson had accepted the invitation to become the next chairman.
"He has extensive experience and is highly regarded within the international business community."
Mr Johnson said GPG's strategic options continued to be evaluated to maximise value for shareholders.
GPG had also established fully operational audit and risk, remuneration and investment committees consisting of non-executive directors.
Shareholders would be updated on the progress of the review of strategic options in February, he said.
