Its theoretical full strength was 3740 men made up of a hussar company, an artillery company and seven 500-man infantry cohorts (3 from Milan, 1 from Cremona and Casalmaggiore, 1 from Lodi and Pavia, 1 from Como and 1 miscellaneous cohort of Italian nationalists, mainly from the Papal States and the Kingdom of Sicily).
It was commanded by the former Milanese nobleman, general Trivulzio and included Ugo Foscolo and Vincenzo Cuoco among its soldiers.
2720 had been recruited by 18 October and on 6 November 1796 it and several other units were ceremonially presented with their standards in the piazza outside Milan Cathedral - they were in red, white and green, which would become the national colours of Italy.
By February 1797 it was stationed in Brescia and on 26 February 1797 it was reorganised into two demi-brigades of three cohorts, an artillery company and a hussar company and at the end of that year the Cisapadane Legion merged into it – that unit had been made up of 6 cohorts of 1,000 men and became the Lombard Legion's third demi-brigade.
The Legion's fourth cohort was attached to General Jean Étienne Championnet's army to fight in Naples in 1798 and the following year the Legion's second demi-brigade formed part of the army of Rome sent to attack the Kingdom of Naples under General Domenico Pino.