Named the Jules Verne, after of the 19th-century French author, the vessel can carry more than 16,000 containers, which would stretch for 90 kilometres end-to-end, and can take more than 180,000 tonnes of cargo.
It is owned and operated by French shipping company CMA CGM, which is the third-largest in the world.
The Jules Verne is 396 metres long and 54 metres wide.
Hollande's visit is the first time a French president has launched a ship since 1960, when the ocean-liner France was put to sea by Charles De Gaulle.
Advances in shipbuilding have led vessels to double in size in the past decade, Yann Alix of maritime industry thinktank Sefacil told RFI.
But French seafarers' unions attack a trend to "gigantism" in cargo ships.
In an open letter to Hollande, the left-wing CGT union says the Jules Verne may increase profits but means higher risks and more serious consequences if it suffers damage.
It tells Hollande that his presence at the launch is an endorsement of the company’s employment of foreign sailors on allegedly poor conditions and “financed by the French taxpayer” and the construction of boats outside the European Union.
CMA CGM already has one massive container-ship, the Marco Polo, which has a crew of just 25, all of them either Croatian or Filipino.