He studied at Otago Boys' High School, and then gained a law degree while working part-time.

He eventually decided to abandon this by moving to Wellington in 1902, but shortly after he arrived, he was invited to return and stand as a parliamentary candidate in Mount Ida, the Otago electorate which encompassed Naseby.

[1] In the 1902 election, Herdman ran on a strongly anti-government platform, harshly criticising the governing Liberal Party.

Herdman believed that the service was poorly organised and subject to political patronage, particularly under the government of Richard Seddon.

[3] In these roles, he gained a reputation as a hard-liner, being described by a contemporary as "ready to employ force ruthlessly for the purpose of upholding law and order".

Both were criticised by many left-wing groups as heavy-handed and repressive, but were defended by the government as necessary steps to preserve order.

[4] In 1935, he resigned from his judicial position to seek re-election to Parliament, contesting the Auckland seat of Parnell.