In 1843, he obtained a commission as Ensign in the 40th (the 2nd Somersetshire) Regiment of Foot, then stationed in India.

In 1844, he purchased the Otago block with Frederick Tuckett on behalf of the New Zealand Company.

He took part in the Flagstaff War and was present at the Battle of Ohaeawai and fall of Ruapekapeka.

The governor transferred an island in the Firth of Thames to Symonds to create a test case regarding the Crown's pre-emptive right of purchase to Māori land deriving from the Treaty of Waitangi; in R v Symonds, the court decided in favour of the Crown's case.

He became a justice of the peace in 1853, was appointed Native Secretary in 1855, and became Onehunga's resident magistrate and returning officer in 1856.