Line 8 was the last line created by the concession of 30 March 1898, and the déclaration d'utilité publique was approved on 6 April 1903.
The project would connect Opéra with Porte d'Auteuil via Grenelle with a shuttle, similar to the network's other lines.
In accordance with the plan to operate Line 7 with a junction on the outskirts of Paris, a branch towards the Porte de Sèvres (today Balard) starting from the Grenelle station was planned to be built subsequently.
The trains would alternately run on the two branches.

Construction of the underwater crossing of the Seine began in April 1908 between the Concorde and Invalides stations, at the level of Pont Mirabeau.
It was finished in January 1911, after a lengthy delay caused by the 1910 flood.
The crossing was routed with a curve 250 metres away.

Although metal caissons were originally planned to be sunk vertically (as had been done on Line 4), a tunnel was drilled following a single circular tube with the aid of a shield; authorities opposed the first method because of the risks to boating.
However, the crossing near Pont Mirabeau was made with vertical caissons.
The Invalides-Javel section was completed in 1910.
The Grenelle station was planned as a double station with platforms on two levels, with the aim to later send trains on the two branches.
However, only one station with a central platform was built, as the Balard branch was planned to be built later.

Before the completion of work near Pont Mirabeau, the line opened to the public on 13 July 1913 between Beaugrenelle and Opéra; the extension to Porte d'Auteuil followed on 30 September.
The Invalides and Concorde stations were still unfinished and opened on 24 December 1913 and 12 March 1914, respectively.
In 1914, the line had fifteen stations between Porte d'Auteuil and Opéra.
Line 8 was the last line created by the concession of 30 March 1898, and the déclaration d'utilité publique was approved on 6 April 1903. The project would connect Opéra with Porte d'Auteuil via Grenelle with a shuttle, similar to the network's other lines. In accordance with the plan to operate Line 7 with a junction on the outskirts of Paris, a branch towards the Porte de Sèvres (today Balard) starting from the Grenelle station was planned to be built subsequently. The trains would alternately run on the two branches.
Construction of the underwater crossing of the Seine began in April 1908 between the Concorde and Invalides stations, at the level of Pont Mirabeau. It was finished in January 1911, after a lengthy delay caused by the 1910 flood. The crossing was routed with a curve 250 metres away.
Although metal caissons were originally planned to be sunk vertically (as had been done on Line 4), a tunnel was drilled following a single circular tube with the aid of a shield; authorities opposed the first method because of the risks to boating. However, the crossing near Pont Mirabeau was made with vertical caissons. The Invalides-Javel section was completed in 1910. The Grenelle station was planned as a double station with platforms on two levels, with the aim to later send trains on the two branches. However, only one station with a central platform was built, as the Balard branch was planned to be built later.
Before the completion of work near Pont Mirabeau, the line opened to the public on 13 July 1913 between Beaugrenelle and Opéra; the extension to Porte d'Auteuil followed on 30 September. The Invalides and Concorde stations were still unfinished and opened on 24 December 1913 and 12 March 1914, respectively. In 1914, the line had fifteen stations between Porte d'Auteuil and Opéra.
Paris Métro Line 8