Peter I Øy lies 450 kilometres from the west coast of continental Antarctica, at position 68° 50′ S, 90° 35′ W. The island is of volcanic origin with an area of 156 km², and it is nearly completely covered by ice. Lars Christensentoppen (1,640 metres) is the highest point on the island. The coastline is completely dominated by a 40-metre-high ice front or by steep cliffs plunging into the sea, which makes landing very difficult. In practice, it is possible to land by boat in only three places. The climate is harsh, with strong winds, low temperatures and snow. For much of the year, thick pack ice surrounds the island.
Vegetation consists almost exclusively of moss and lichen species that have adapted to the extreme Antarctic climate. Some seabird species, notably the southern fulmar, nest in a couple of places on the island, and a small penguin colony has been observed.
Many seals (especially crabeater seals and leopard seals) are found both on land and in the surrounding waters.