On 3 March 1749 Boulton married Mary Robinson, a distant cousin and the daughter of a successful mercer, and wealthy in her own right. They lived briefly with the bride's mother in Lichfield, and then moved to Birmingham, where the elder Matthew Boulton made his son a partner at the age of 21. Though the son signed business letters "from father and self", by the mid-1750s he was effectively running the business. The elder Boulton retired in 1757 and died in 1759.