In 1887 McKinnon was employed by the Otago Survey Department to try to find a tourist route into Milford Sound.
Included in the party were Thomas Mackenzie, William Soltau Pillans, and the commercial photographer, Fred Muir.
McKinnon was successful and discovered a passage between the head of Lake Te Anau and Milford Sound.
After the discovery of the pass McKinnon spent time improving the track and taking regular parties of sightseers and tourists through the area.
A public subscription was raised to build the Quintin MacKinnon Memorial Cairn which stands at the summit of McKinnon Pass.