William Donald Stuart MacDonald (1862 – 31 August 1920) was a New Zealand politician, Cabinet Minister, and briefly Leader of the Opposition.

He then managed land at Papatu before doing likewise at two properties owned by Alexander Creighton Arthur at Matawhero and Whatatutu.

On one such occasion in May he called a caucus meeting to discuss the coalition between the Liberal and Reform parties where a majority of members voted in favour of ending the arrangement upon Ward's return.

MacDonald was himself unsure the correct decision was reached and he cabled Ward for his opinion, who agreed with the consensus in the caucus.

Consequently, MacDonald worked with his colleagues (particularly George Warren Russell and Thomas Wilford) to develop an updated policy manifesto for the next election.