In 1845 he married Johanne Margrethe "Hanna" Bull Kielland (1823-1908), youngest daughter of Jacob and Axeliane Christine Kielland and aunt of novelist Alexander Lange Kielland and painter Kitty Lange Kielland. The couple had three daughters and seven sons. Of these children one died young. Their most prominent child was painter Jacob Kielland Sømme. Their oldest daughter married jurist Ove Høegh Gude. Their sons Axel Christian Zetlitz and Andreas were businessmen, the latter was also the father of geographer Axel Christian Zetlitz Sømme. Two other sons Jonas Christian and Erling were jurists, Jonas Christian Sømme was also a local politician. The youngest son Johannes Kielland Sømme became a consul.
Sømme was also involved in local politics, as mayor of Stavanger in 1859, 1860 and 1869.