Caldwell was an active member of the
Women's Suffrage League and consistently presented and supported Bills to extend the franchise to women. On one point his conservative views caused him to disagree with the League as Caldwell believed only women of property should be allowed to vote, rather than all women which was the League's position. Caldwell kept the issue at the forefront of debate in Parliament through separate franchise bills in 1888, 1889 and 1890. Reporting on parliamentary debates and subsequent discussions in the wider society thus provided opportunities for the Women's Suffrage League to strengthen their campaigning, which led to South Australian women receiving the vote
in 1894.
Mary Lee, a founding member and Honorary Secretary of the
Women's Suffrage League, described Caldwell as a courageous champion of the League for his persistence in keeping the issue before Parliament. ==Publications==