Career
He held the seat only until Parliament was dissolved later that year for the 1885 general election, when the two-seat Antrim constituency was divided into four single-member divisions. Sinclair stood in North Antrim, where in a three-way contest he was defeated by the Conservative Edward MacNaghten. When the Liberal Party split in 1886 over Irish Home Rule, Sinclair joined with the breakaway Liberal Unionist Party, and was elected at the 1886 general election as Member of Parliament for Falkirk Burghs in Scotland, with a majority of only 19 votes (04% of the total) over the Liberal Party candidate.
He lost the seat to the Liberals at the 1892 general election, and did not stand for Parliament again.