Moorhead was a member of the Legislative Assembly of Western Australia from 1899 to 1901, and briefly served as the state's attorney-general in the government of Alf Morgans.

A representative of Dublin University A.F.C., he played a single match for the Irish national team, appearing against England during the 1884–85 British Home Championship.

[1] Moorhead first attempted to enter parliament at an 1895 Legislative Council by-election for Central Province, but lost to William Alexander (by only seven votes).

Under the state constitution at the time, newly appointed ministers were required to resign and recontest their seats in a ministerial by-election.

Moorhead and two other ministers (Matthew Moss and Frank Wilson) were defeated, resulting in the collapse of the Morgans government after just over a month.

[5] In April 1902, Moorhead was appointed as a puisne judge of the Supreme Court, joining Edward Stone (the chief justice), Alfred Hensman (who died in October 1902), and Stephen Henry Parker on the bench.