Wallace Hewetson (also Hewitson) was a son of Charlton Hewetson and his wife Charity. He was employed in farming as a young man and then served for some years as a soldier in the Irish Lancers. On leaving the army he did church work as a lay reader in Ipswich and Norwich, England, which led to his being sent to South Africa to assist Reverend Francis Owen of the Church Missionary Society, who was establishing a mission amongst the Zulus at Dingaan's kraal. Hewetson landed at Algoa Bay with his family in December 1837 and, travelling overland, reached Port Natal (now Durban) on 8 March 1838. He was to instruct the indigenous people in agriculture. However, as a result of the unsettled state of the country Owen had abandoned his mission and the party (including Owens' sister, Miss M.C. Owen*) left Natal in May that year. They remained for some time in Port Elizabeth, where Owen and Hewetson opened a school.
During his brief stay in Natal Hewetson made a small collection of plants, probably at the request of William H. Harvey*, who was just able to acknowledge receipt of Hewetson's specimens in his Genera of South African plants (1838). Hewetson is also known to have collected plants at Port Elizabeth.
In 1839 the mission party travelled across the Vaal River to open a mission station among the people of the fugitive Zulu chief Mzilikazi at Mosega, south of Zeerust, where they arrived in December. Hewetson successfully grew maize and potatoes there, but in 1841 the mission had to be abandoned. Owen and his sister returned to England, but Hewetson remained in the country. He first farmed near Bedford without much success and then at Belmont, near Grahamstown, but the Frontier War of 1845 forced him to move to town where he entered the service of Messrs Cawood. In 1846 the firm sent him to King William's Town as their agent. Here he opened his own business and later established a trading store at Gonubie. In 1850 war again forced him to move and he settled in King William's Town. He was a popular person, tall and erect, with an Irish sense of humour. He was married to Anne Mason, with whom he had seven children. His letters and journals during 1837-1841 are kept in the archives of the Church Missionary Society.