The 1899 Northumberland colonial by-election was held on 20 June 1899 to elect the member for Northumberland in the New South Wales Legislative Assembly, following the death of Protectionist MP Richard Stevenson. The vote was held on the same day as a statewide referendum on the subject of federation, which was an issue throughout the campaign.
Two candidates withdrew during the campaign. On 9 June 1899, Protectionist-endorsed candidate William Schey withdrew shortly after candidate nominations closed to avoid splitting the vote with Independent Protectionist candidate John Norton. Five days later, William Melville withdrew and endorsed fellow Federalist candidate William Snape.
Norton won the seat with 52.6% of the vote, defeating Free Trade candidate (and former Northumberland MP) Henry Wheeler.