A 30-year-old Iraqi, considered the group leader, received an 18-month sentence from the court in Boulogne, on the northern French coast.
His two accomplices, a 30-year-old Iranian and a 39-year-old Iraqi, were each jailed for a year and all three men were banned from French territory.
French border police were first alerted when the manager of a boat supply store contacted them in December over suspect sales of inflatable dinghies, a vessel of choice for people smugglers transporting migrants and refugees from France to Britain.
The subsequent enquiry implicated the three suspects in the organisation of migrant boat runs from several northern French ports including Calais and Sangatte.
Some 500 people — most of them over the last two months of 2018 — attempted to cross the Channel to Britain last year, compared with just 13 known attempts in 2017.
London in December dispatched a navy ship to help coastguard boats watch
over the 33 kilometres of sea that separate France and Britain at its narrowest point.
France also responded by announcing broader surveillance measures in early January.
The number of Channel crossings was just a tiny fraction of the 55,756 successful attempts made across the Mediterranean to Spain that were recorded by the UN's refugee agency in 2018.