The Soviet period (1917–1991) saw a rapid population increase, although most of the new arrivals remained confined to urbanized territories along the sea coast and the railroads.

The Sami people were subject to forced collectivization, including forced relocation to Lovozero and other centralized settlements, and overall the peninsula became heavily industrialized and militarized, largely due to its strategic position (as the pre-eminent Soviet ice-free Atlantic coast) and to the discovery of the vast apatite deposits in the 1920s.

The peninsula is covered by taiga in the south and by tundra in the north, where permafrost limits the growth of trees, resulting in landscape dominated by shrubs and grasses.

[3] The mountainous reliefs of the Murman and Kandalaksha Coasts stretch from southeast to northwest, mirroring the peninsula's main orographic features.

[3] In the tundra, cold and windy conditions and permafrost limit the growth of the trees, resulting in a landscape dominated by grasses, wildflowers, and shrubs such as dwarf birch and cloudberry.

[14] Twenty-nine species of fresh water fish are recognized on the territory of peninsula, including trout, stickleback, northern pike, and European perch.

[11] The rivers are an important habitat for the Atlantic salmon, which return from Greenland and the Faroe Islands to spawn in fresh water.

[19] Additionally, several nuclear weapons test ranges and radioactive waste storage facilities exist on the peninsula.

The ultimate aim is a 95% reduction (compared to 2015) in SO2 by 2030 for its Polar Division on the Taimyr peninsula, which includes its Nadezhda smelter and Copper plant, partly through a SO2 capture solution.

[25] Bolshoy Oleny Island in the Kola Bay of the Barents Sea is the location of an important Bronze Age archaeological site where ancient DNA has been recovered.

[26] By the end of the 1st millennium CE, the peninsula was settled only by the Sami people, who did not have their own state, lived in clans ruled by elders,[27] and were engaged mostly in reindeer herding and fishing.

[28] In the 12th century, Russian Pomors from the shores of the Onega Bay and in the lower reaches of the Northern Dvina discovered the peninsula and its game and fish riches.

[27] Pomors were soon followed by tribute collectors from the Novgorod Republic, and the Kola Peninsula gradually became a part of the Novgorodian lands.

[30] The treaty did not address the situation with the Sami people paying tribute to both Norway and Novgorod, and the practice continued until 1602.

[30] Over time, all coastal areas to the west of the Pyalitsa River had been settled, creating a territory where the population was mostly Novgorodian.

In the second half of the 16th century, the peninsula became a subject of dispute between the Tsardom of Russia and the Kingdom of Denmark–Norway, which resulted in the strengthening of the Russian position.

By the end of the 19th century, the indigenous Sami population had been mostly forced north by the Russians as well as by newly arriving Izhma Komi and Kominized Nenets (so-called Yaran people), who migrated here to escape a reindeer disease epidemic in their home lands in the southeast of the White Sea.

[8] 1887 saw an influx of Izhma Komi and Nenets people who were migrating to the peninsula to escape a reindeer-disease epidemic in their homelands and brought their large deer herds with them, resulting in increased competition for the grazing lands, a conflict between the Komi and the Sami, and in marginalization of the local Sami population.

[32] By the end of the 19th century, the Sami population had mostly been forced north, with ethnic Russians settling in the south of the peninsula.

[8] Also in 1896, Alexandrovsk (now Polyarny) was founded, and grew in size so rapidly that it was granted town status in 1899; Kolsky Uyezd was renamed Alexandrovsky on that occasion.

[33] During World War I (1914-1918), the still poorly developed peninsula suddenly found itself in a strategic position, as communication between Russia and the Allies via the Baltic and Black Sea was cut.

Britain helped in the development of the ice-free harbors of the Murman Coast as the only practical means of sending Allied war supplies to the Eastern Front.

[8] In 1916, Romanov-na-Murmane (Romanov on the Murman: modern Murmansk) was founded[33] as the terminal point of the new railroad;[8] the town quickly grew to become the largest one on the peninsula.

[39] Prisoner labor was often used when building new factories[40] and for manning those which were operational: in 1940, for example, the whole Severonikel Metallurgy Mining Complex was turned over to the NKVD system.

[28][43] However, the discovery of the vast natural resource deposits and industrialization efforts led to an explosive population growth during the Soviet times.

[19] During the 15th–16th centuries, the main occupations of the Tersky Coast population were Atlantic salmon fishing, seal hunting, and the extraction of salt from the sea water.

[25] The salt extraction in Kandalaksha and Kola was mostly carried out by the monasteries in Pechenga and Solovki, and for a long time remained the only "industry" on the peninsula.

[48] The consolidations were rationalized by the necessity to isolate the herders from the military installations, as well as by the need to flood some territories to construct hydroelectric plants.

[48] Fishing, being the traditional industry of the region, was always considered important although the volumes of production remained insignificant until the beginning of the 20th century.

[54] The Kola Mining and Metallurgical Company, a division of Norilsk Nickel, conducts nickel-, copper-, and platinum-group-metals-mining operations on the peninsula.