The town-based building society, which employs 122 people, recorded £88million of new mortgage lending last year.
That contributed to total assets of £427million and an “all-time high” profit before tax of £2.9million.
Chief executive Mark Robinson said: “We are investing in future growth, whilst keeping a firm hold on our traditional values, ensuring that MHBS remains a safe and secure home for its members.
“We are proud to remain focused in offering a unique personal customer service.”
The building society has six branches and one agency and 35,000 savers, many of whom live in south Leicestershire and north Northamptonshire. It also has 4,000 mortgage members.
Most staff are based in Market Harborough, occupying offices around the former Working Man’s Club site off Northampton Road.
Louise Bunce, head of sales and marketing, said that a more nimble, individual approach to mortgage lending has helped the building society prosper against the “computer says no” approach of larger firms.
The society, founded in the town in 1870, operates nationally, but also sponsors local events like Pride in Harborough, Harborough by the Sea, the Carnival of Running and Arts Fresco.