The island was uninhabited until the early 20th century, when Aleuts came from Attu Island in the Aleutian Islands to Medny Island.
The island is 56 km long and between 5 and 7 km wide and its area is 186 km². Its maximum elevation is 640 m and the average annual temperature is +2.8 °C. About 100 meters off the northwestern end of the islands are the Beaver Stones, two islets connected by an isthmus, with a combined length of 1 km.
The island was sighted by on 5 November 1741 by Bering and his crew while returning from the expedition during which he found America from the west, but he did not land on this island.
The Russian naval officer and historian Vasily Berch believed that Yemelyan Basov reached this island in 1745, during his second of four expeditions to the Commander Islands between 1743 and 1749, and that most of the furs he brought back to Kamchatka in 1745 were hunted on this island.
Towards the end of the 19th century, the settlement of Preobrazhenskoye was established by Aleuts who moved there from Attu Island.
In 1970, all citizens of the island were moved to neighboring Bering Island. Until 2001, the island was occupied as a frontier post. Since then, the island has been completely uninhabited. Scientific studies of the fauna and flora are conducted annually.
Medny Island is home to many Steller sea lions. 340 pups were born on the island in 1999, and 153 in 2016.