The appointment at the Sussex-based chartered accountants, tax and business advisers, took effect this month.
The MHA Carpenter Box Wealth Management team has expanded from eight to 11 and now provides investment solutions for around 450 clients.
Growth is expected to continue with a plan to recruit two new members of staff this year.
Mr Thompson joined the firm’s wealth management team in 2011, as a financial adviser and has progressed to partner having previously been a departmental director at the company.
He also worked at Clydesdale Bank for six years as a Senior Financial Planner and at HSBC Bank as a Financial Planning manager.
As well as looking after his own client base, Mr Thompson is responsible for overseeing the client experience provided by the wealth management team.
His particular area of expertise is in providing pensions advice.
He said: “I have always enjoyed a challenge and with new products frequently being introduced and new legislation continually impacting on regulated firms, working in the financial sector is certainly that.
“I continue to enjoy meeting people and analysing what they are looking for in terms of an investment and then finding the right solutions for them.
“I’m looking forward to growing the wealth management team and continue to deliver and build on the already high standard of client care and service that we provide.”