In 1862, when he was the Interior Minister of Argentina, he met Captain Love Jones-Parry and Lewis Jones, who were on their way to Patagonia to investigate whether it was suitable for the creation of a Welsh settlement there.

After a Jesuit education in San Juan, Rawson graduated from the Medical Faculty of University of Buenos Aires in 1844.

In 1853, he was jailed for opposing Nazario Benavidez, the caudillo or de facto governor of San Juan.

The following year he was a member of the Paraná Congress, and from 1862, he was Interior Minister in the government of Bartolomé Mitre.

The building of the first medical school in Buenos Aires is named Escuela Dr Guillermo Rawson in his honour.