In 1929 he was nominated as one of two Labour candidates for the two-seat Oldham constituency along with James Wilson.[1][4] The general election saw a large swing to the Labour Party, and Lang and Wilson were elected, unseating the two sitting members (one Conservative and one Liberal.)[5]
In 1937, Philip Dunne, the Conservative MP for Stalybridge and Hyde retired due to ill health. Lang was chosen to contest the ensuing byelection, which was a straight fight with Horace Trevor-Cox, Conservative and National Government candidate.[9] Lang came close to winning the seat, reducing the Conservatives' majority from the 1935 general election of 5,081 votes to just 334.[10]
With the outbreak of the Second World War in 1939, elections were postponed. It was not until 1945 that another general election was held. Lang and Trevor-Cox were again the candidates of the Labour and Conservative parties respectively, joined by a Liberal candidate, Donald Burden.[11] The 1945 general election resulted in a Labour landslide victory, where the first majority Labour government was formed, and Lang was comfortably elected with a majority of 4,370 votes.[12] He retained the seat at the next general election in 1950.[13] The result of the election was a reduced Labour majority, and another general election was called in 1951 to increase it. Lang announced that he would not contest the election due to ill health, and retired from the House of Commons.[14]