Educated at Orere School and King's College, Cashmore with his father and brother on their family farm until taking over as owner and manager in 1989.

Cashmore's political career began when he was elected as a member of the Clevedon community board in 1991.

[citation needed] In 2010 he became the Federated Farmers executive for the Auckland Province and a representative to the Animal health board.

In 2013 he was elected as an Auckland Councillor, replacing the incumbent, Des Morrison, who had retired.

In 2015 he became the chair of the Audit and Risk Committee and a member of the Political steering group for the Auckland Transport Alignment Project.