A by-election was held for the New South Wales Legislative Assembly electorate of Mudgee on 6 January 1879 because of the resignation of Sir John Robertson who was then appointed to the Legislative Council, to facilitate the coalition of his supporters and those of Sir Henry Parkes to form an effective government.
<includeonly> Sir John Robertson resigned to be appointed to the Legislative Council.</includeonly>
In March 1879 the Committee of Elections and Qualifications overturned the election of Richard Rouse and declared that David Buchanan was elected as the member for Mudgee.