Chewings was selected on 17 September 1969 as the National Party candidate for the Invercargill electorate in the 1969 election, following the death of Ralph Hanan in July.[2] He represented Invercargill until 1972, when he was defeated.[3] He was one of four National Party incumbents from Otago and Southland who lost their normally blue electorate to the Labour challenger over the proposed raising of the lake levels of lakes Manapouri and Te Anau, which was opposed by the Save Manapouri campaign. Labour's election manifesto was for the lakes to remain at their natural levels.[4]