The expanded society will be called Coventry Building Society and will be based in Coventry.
Total membership will increase from over 1.2m to around 1.5m and the overall asset size will increase from £18.4bn to £21.1bn.
Coventry expects a third of about 250,000 savings accounts will see improved interest rates on completion of the merger, to match equivalent products it offers.
It adds borrowers currently paying or linked to Stroud & Swindon’s residential Standard Variable Rate (SVR) of 5.99% will benefit from a cut in their mortgage payments as they move onto Coventry’s lower SVR of 4.74%.
David Stewart, chief executive of Coventry Building Society, said: “Coventry’s performance over the last three years has demonstrated the strength of our traditional building society model.
“I believe the merger with Stroud & Swindon will help us build on recent successes and bring the benefits of our prudent and member-focused approach to a wider membership.”
