Tomos — an acronym of Tovarna Motornih koles Sežana, meaning Motorcycle Factory Sežana — was established by the Yugoslav government in the town of Sežana in July 1954, shortly after the decision was taken to develop new industries in post-war Yugoslavia. The name appeared in company documents in August 1954, and the Koper factory construction began in October. Production started in temporary facilities in 1955, and the factory was formally opened in 1959 by Yugoslav president Josip Broz-Tito.
The founding licensing agreement with the Austrian firm Steyr-Daimler-Puch gave Tomos access to Puch's motorcycle and moped designs, which were well suited to the mountainous terrain and rough roads of the region. Puch offered favourable terms in part because it doubted the Yugoslav factory would ever operate independently. The first Tomos product was a motorcycle called the Tomos Puch SG 250, and initial output included motorcycles, scooters, and mopeds, with mopeds quickly becoming the dominant product category.
In the late 1950s, Tomos produced multiple variants of the Puch MS 50 under the collective name Colibri, with the type 12 among the most successful and the Colibri T 12 becoming the most popular moped in Slovenia after its 1961 introduction. By 1959, Tomos was manufacturing more than 17,000 Colibris per year and had signed a major export contract with Sweden.
The 1960s were Tomos's most productive decade. The Netherlands emerged as a key market from 1960, and in 1966 a second Tomos plant opened in Epe in the Netherlands to serve Dutch demand. This Dutch operation, which included its own research and development team responsible for models such as the Colibri, Targa, and Revival, became the longest-surviving moped factory in the Netherlands, outlasting at least 36 other manufacturers before production ended there in 2009. Tomos entered the American market in 1976 and continued selling mopeds in the United States until 2014, while also exporting to Canada and, from 2017, to the United Kingdom.
Alongside its production activities, Tomos participated in the 50cc class of the Motorcycle World Championship, the smallest-displacement category contested under Grand Prix regulations. The 50cc World Championship had been established in 1962, and small national manufacturers from Europe competed against the dominant Spanish and Japanese factories throughout the 1960s and 1970s. Tomos fielded machines in this category and gathered results in a competitive class.
From the early 1970s, Tomos began developing its own engine designs to replace licensed Puch units, responding to rising component import costs. The Automatic A1 was the first in-house-engined model, with the modernized Automatic A3 following in 1973 on a new welded framework production line. After 1973, all Tomos two-wheelers used engines of Tomos's own manufacture. New Colibri models continued through the decade, with the Colibri 14V being the first to use a Tomos-designed motor.
The oil crisis of the late 1970s created temporary demand spikes in fuel-efficient transport, with the US moped market peaking in 1979. Tomos responded with modernization programs through the 1980s aimed at reducing noise and emissions and improving rider comfort. New-generation models such as the APN 6 appeared in 1981 and the BT 50 in 1985.
Beginning in 1959, Tomos produced Citroën automobiles under license at the Koper plant for the closed Yugoslav market. In 1972, Tomos, Iskra, and Citroën formed a joint company called Cimos for manufacturing and exporting cars and automotive components. Cimos produced locally variants of the Ami 8, 2CV6, GS, Dyane (marketed as the Diana), and other Citroën models, as well as developing unique utility vehicles — the Dak cargo van and the Geri pickup truck — from 2CV-based platforms. The Cimos venture collapsed after 1985 when parts supply from Citroën was cut following disputes over export restrictions.
Tomos remained state-owned until 1998, when it was privatized and sold to Hidria, a private Slovenian corporation. Following Slovenian independence in 1991, all Tomos products carried "Made in Slovenia" labelling. The company continued producing mopeds into the 2010s and briefly returned to the US market with the redesigned Sprint and the Racing TT, but could not sustain profitability against Asian competition. Tomos declared bankruptcy on 3 January 2019.