Marchissy is a municipality in the Swiss canton of Vaud. It is located in the district of Nyon.
Marchissy is first mentioned in 1235 as Marchisie.
Marchissy has an area, as of 2009, of 11.98 square kilometers (4.63 sq mi). Of this area, 3.82 km2 (1.47 sq mi) or 31.9% is used for agricultural purposes, while 7.76 km2 (3.00 sq mi) or 64.8% is forested. Of the rest of the land, 0.35 km2 (0.14 sq mi) or 2.9% is settled (buildings or roads), 0.01 km2 (2.5 acres) or 0.1% is either rivers or lakes.
Of the built up area, housing and buildings made up 1.3% and transportation infrastructure made up 1.3%. Out of the forested land, 62.3% of the total land area is heavily forested and 2.5% is covered with orchards or small clusters of trees. Of the agricultural land, 15.0% is used for growing crops and 5.3% is pastures and 11.2% is used for alpine pastures. All the water in the municipality is flowing water.
The municipality was part of the Aubonne District until it was dissolved on 31 August 2006, and Marchissy became part of the new district of Nyon.