Benelli was established in Pesaro, Italy in 1911, which makes it maybe the oldest of all European motorcycles factories in operation. (Moto Guzzi - the oldest European motorcycle factory in non-stop operation - was established in 1921.) After losing her husband, the widow Teresa Benelli invested all of the family capital into the business in the hope that it would offer stable work for her six sons: Giuseppe, Giovanni, Francesco, Filippo, Domenico and Antonio ("Tonino"). She also sent Giuseppe and Giovanni to study Engineering in Switzerland. Initially the business had 6 employees in addition to the 5 brothers working (Tonino didn't work because he was too young.)

In the beginning, it was just the Benelli Garage, which repaired bicycles and motorcycles, but was already able to produce all of the spare parts needed for repairs.[2] During World War I, Benelli worked hard fixing parts for the Italian machines in war and in 1919 the first motorcycle was presented to the public. In 1920 the company built its first complete engine in-house, a single-cylinder two-stroke 75 cc model, immediately adapted to a bicycle frame. A year later in 1921, Benelli built its first motorcycle, using their own engine which had by then become a 98 cc model.

Two years after that, using a version specially designed for competitions, Tonino "the terrible" took to the track. He displayed an extraordinary natural talent as a rider and embarked on a very successful career which confirmed the company's exceptional capacity for development and production. Riding a Benelli 175, Tonino Benelli won four Italian championship titles in five years: in 1927, 1928 and 1930 with the single overhead camshaft (SOHC) version, and in 1931 with the double overhead camshaft (DOHC) version. Unfortunately, a bad crash during a race in 1932 cut short his brilliant career and on 27 September 1937 Tonino died following a "silly" road accident.

As World War II loomed, the Benelli company debuted their four-cylinder supercharged 250cc racing bike. This was intended to compete in the 1940 season, building on Benelli's success in the 1939 Isle of Man TT Lightweight 250 cc race. With the start of the war, the Benelli Four was limited to competition in a handful of Italian domestic races.

Towards the end of the 1960s, the arrival of Japanese manufacturers caused a crisis in the European motorcycle industry. The original Benelli company was heavily involved in the American motorcycle market, selling motorcycles under 350cc through Montgomery Ward. The advent of competition from Japan led to Benelli products (still largely of single cylinder pushrod design) losing popularity as they were perceived as old-fashioned in comparison to Hondas of the era which sported overhead cam engines with electric starters, in much the same way as the British motorcycle manufacturers such as Norton, BSA and Triumph were affected in the larger capacity sector.