Prendergast was one of the first Labor members of the Victorian Legislative Assembly, being elected for North Melbourne in 1894. In September 1897, Prendergast was arrested and charged with obstructing a footpath on Bourke Street, Melbourne, after he refused to move when instructed to by a police officer—the case was dismissed by the court. At the 1897 election, Prendergast was defeated by William Watt, but regained the seat in 1900, and held it until it was abolished in 1927. He then shifted to the electorate of Footscray, which he represented until his death. In all he was an MP for 40 years, but was noted more for his fiery stump oratory than any real ability: the historian Kate White calls him "mediocre." In 1904 Prendergast became the first leader of the Parliamentary Labor Party. He resigned this position through ill-health in 1913, allowing George Elmslie to become the first Labor Premier, and was Chief Secretary in Elmslie's 14-day government. He returned to the Labor leadership in 1918. He was the President of the North Melbourne Football Club for some time. Victoria was Labor's weakest state throughout the 1920s, due to the gross over-representation of rural areas in the Legislative Assembly, and the strength of the Country Party in rural areas and the Nationalist Party in middle-class Melbourne seats. Labor's parliamentary representation was confined to the industrial areas of Melbourne and a few provincial towns. There was little talent in the Parliamentary Labor Party and few regarded Prendergast as likely ever to win a state election. In April 1924, however, the Country Party withdrew its support from the Nationalist government of Alexander Peacock when he tried to pass a bill reducing rural representation. Peacock called an election in June, at which Labor won 27 seats, the Nationalists 20 and the Country Party 13. Labor offered a series of policy concessions to the Country Party, and the party agreed to support a minority Labor government. Prendergast thus became Premier at the age of 70 – the oldest man ever to take the officefor the first time. The only real talents in his government were Edmond Hogan as Minister for Agriculture and Railways and William Slater as Attorney-General. John Cain was an Assistant Minister. Prendergast's government was the first Labor government in Victoria able actually to govern. Immediate action was taken to provide shelter for unemployed Victorians, while the government set up royal commissions into the causes of a major police strike in 1923, the prices of bread and flour, and the soldier settlement scheme. Increased expenditure was made available for rural roads, while reductions were made on rail freights and fares. With the support of the Country Party, he was able to pass several bills assisting farmers, but the Country Party would not support anything which benefited Labor's urban working-class base. This was a frustrating situation for Labor ministers, and several urged Prendergast to call another election in the hope of improving their position, but Prendergast was too timid to run this risk. In November the Country Party patched up its differences with the Nationalists, and the two parties joined forces to defeat Prendergast in the Assembly. The Country Party leader, John Allan, succeeded him as Premier.
Last years
Prendergast resigned as Labor Leader in 1926 and was succeeded by Hogan. In Hogan's first minority government he was again Chief Secretary. He died in 1937, still an MP, aged 83.
