Robert McMillan may refer to:

• Robert S. McMillan (architect) (1916–2001), architect and co-founder of The Architects Collaborative
• Robert S. McMillan (astronomer), astronomer at the University of Arizona
• Robert McMillan (Australian judge) (1858–1931), Chief Justice of the Supreme Court of Western Australia
• Robert Johnston McMillan (1885–1941), U.S. federal judge
• Robert Thomas McMillan (1887–1962), member of the New Zealand Legislative Council
• Robert McMillan (footballer) (1857–1928), Welsh footballer
• Robert MacMillan (1865–1936), Scottish national rugby union player
• Bob MacMillan (born 1952), Canadian hockey player and politician

• Robbie Coltrane (actually Anthony Robert McMillan, 1950–2022), Scottish actor
• McMillan (surname)