In February 1917 he won ALP pre-selection for a
by-election in the seat of
Sturt. The by-election had been caused by the resignation of the previous member
John Cann who had accepted the position of Railways Commissioner. Brookfield won the seat with 54% of the primary vote and increased this to 57% at the general election that was held one month later. In parliament he became a leading left-wing advocate and expressed sympathy for the
Industrial Workers of the World and the
Bolshevik Revolution. His radicalism led him into conflict with the rest of the ALP caucus and he resigned from it in July 1919. He was not readmitted to the party when he attempted to retract his resignation. He later then joined the
Industrial Socialist Labor Party. At the March 1920 state elections Brookfield contested the seat of Sturt for the
Socialist Labor Party after its amalgamation with the Industrial Socialist Labor Party, and, under the multi-member proportional representation system then used, he was the first candidate elected with 27% of the primary vote. Following the election, he held the
balance of power in the assembly. He supported the Labor government of
John Storey and used his position to improve industrial conditions for Broken Hill miners and to overturn the convictions of Australian IWW members gaoled in 1916. In February 1921, Brookfield and several other members left the Socialist Labor Party to reform the independent Industrial Socialist Labor Party. ==Death==