Sinclair joined the firm on 1 February as chief operating officer and he will take up his additional executive responsibilities to the board from 1 April.
Polin has been heading up a revamp at the wealth manager since he joined at the start of September following his departure from Ignis Asset Management.
His main priority is to return the firm to profitability and back in December he ploughed £200,000 of his own money into the company.
Now the largest shareholder of the business, with a 0.74% holding in total, Polin has an even greater motivation to succeed in his review strategy.
A source within the firm said he felt Polin had done a good job so far and had implemented change that had been needed for some time.
In today’s appointment statement, Polin said: "Despite having only been with us for a relatively short period of time, he [Sinclair] has already had a significant impact on the way the business operates today and crucially how it is being structured for the future.
"By inviting Richard to join the board we are ensuring the business gets the maximum benefit from his energy and experience as we seek to develop and grow the business into a leading UK wealth manager over the next five years."
