Donald McMillan or MacMillan may refer to:
- Donald McMillan (Ontario politician) (1835–1914), Senator from Ontario
- Donald McMillan (Quebec politician) (1807–1876), who represented Vaudreuil in the 1st Canadian Parliament
- Donald Baxter MacMillan (1874–1970), American explorer
- Donald MacMillan (rugby union) (born 1930), rugby union player who represented Australia
- Don MacMillan (1928-2004), Australian Olympic athlete