Lang Labor was a faction of the Australian Labor Party (ALP) consisting of the supporters of Jack Lang, who served two terms as Premier of New South Wales and was the party's state leader from 1923 to 1939. It controlled the New South Wales branch of the ALP throughout most of the 1920s and 1930s. The faction broke away to form separate parliamentary parties on several occasions and stood competing candidates against the ALP in state and federal elections.

John Thomas Lang, usually referred to as J. T. Lang during his career and familiarly known as "Jack" and nicknamed "The Big Fella", was an Australian politician, mainly for the New South Wales Branch of the Labor Party. He twice served as the 23rd Premier of New South Wales from 1925 to 1927 and again from 1930 to 1932. He was dismissed by the Governor of New South Wales, Sir Philip Game, at the climax of the 1932 constitutional crisis and resoundingly lost the resulting election and subsequent elections as Leader of the Opposition. He later formed Lang Labor that contested federal and state elections and was briefly a member of the Australian House of Representatives.