Born at Tewkesbury, Winterbotham was one of eight surviving children of a Stroud banker and his wife, the daughter of a Baptist minister.
Winterbotham enjoyed ‘an exceptionally brilliant’ academic career at the University of London, becoming Hume scholar in jurisprudence, 1858, and political economy, 1859, and taking the university law scholarship and gold medal. After being called to the bar he went on the Oxford circuit and practiced at the chancery bar, acting as a conveyancer until 1871.
In January 1867 Winterbotham came forward for Stroud in anticipation of an early dissolution after the long-standing Liberal member, George Poulett Scrope, intimated an intention to retire. As a member of a much respected local family, Winterbotham was regarded as a popular alternative to the other sitting Liberal, Edward Horsman, who had long been unsympathetic to parliamentary reform.
Although Winterbotham had declared himself ‘a consistent member of the liberal party’, he chose to sit ‘among the more advanced politicians’ below the gangway.
Notwithstanding strong personal attacks over his support for the disestablishment of the Irish Church, Winterbotham was said to be popular with the ‘intelligent working men’ of Stroud, and easily defeated a Conservative to take second place in the poll at the 1868 general election.
