When Mohkam Singh died in 1841 without leaving any issue of the body or an adopted heir, the throne of Kishangarh became vacant. That same year, Mohkam's widow formally adopted Prithwi as her son, and he succeeded Mohkam on the throne of Kishangarh. Throughout his reign, he conducted the administration of his state with competence and success. He laid the foundation upon which administrative reforms were later introduced in Kishangarh.
Death
He died in 1879 and was succeeded by his son, Sadul Singh, as the Maharaja of Kishangarh.
Titles and styles
His fullstyle was: "His Highness Umdai Rajahai BulandMakan Maharaja Shri Prithwi Singh, Maharaja of Kishangarh."