Robertson was the endorsed Labor candidate for the seat of Dubbo at the 1941 election. Despite a resurgence in rural support for Labor at the election, Robertson was defeated by the incumbentCountry Party member George Wilson by 159 votes. Wilson died 11 months after the election and Robertson won the resultantby-election. He retained the seat for Labor for 8 years but was defeated, during a general swing against Labor, at the 1950 election by Robert Medcalf the incumbent Country Party member for Lachlan. Medcalf's seat had been abolished by a redistribution. Robertson regained the seat in 1953 and retained it until he was defeated at the 1959 election by the Liberal Party's, Les Ford. Robertson joined the Country Party in 1961 in the expectation that he would be the party's candidate at the election held in March 1962. However, the party did not endorse a candidate and Robertson styled himself as the "Independent Country" nominee. He received 5% of the vote and retired from public life. He did not hold party, parliamentary of ministerial office. After leaving parliament he owned and managed a farm.