Thomson joined the Edinburgh-based mutual from Scottish Widows Bank last year and succeeds Gerry Kay, who stepped down last month after five years as chief executive.
The lender, which completed its merger with Scotland’s smallest mutual – Century Building Society – in February, has a £277 million mortgage book 67 branches and agencies across Scotland.
Thomson, a chartered banker, has 30 years’ experience in the finance sector and spent the early part of his career at Bank of Scotland and Royal Bank of Scotland.
He said: “I answer to 37,000 members and a dynamic board of directors and I aim to build on the good work of recent years, which has seen growth in assets and in mortgage business, and I know we can do this whilst continuing to treat our members fairly.”
The Scottish Building Society, founded in 1848 as the Edinburgh Property Investment Company, is the country’s oldest mutual.