Born at Carrs Plains to grazier Holford Wettenhall (a former Legislative Council member) and Mary Burgess Dennis, he attended local state schools before attending Toorak College and Geelong College, becoming an orchardist, wheat farmer and grazier.
On 27 January 1903 he married Leila Ashton Warner at Hobart, Tasmania; they had five children.
Wettenhall joined the People's Party in 1912 to oppose the creation of the Commonwealth Bank of Australia, although he later reversed his opposition.
In 1920 he was elected to the Victorian Legislative Assembly as the Country Party member for Lowan.
He was defeated in 1935 when the Country Party allowed two candidates to contest the seat, which was won by Hamilton Lamb.