Line 8 is 22.057 km (13.706 mi) long, including 2.8 km (1.7 mi) of open-air tracks in the southeastern suburbs.
It is the second-longest line (after Line 13), with the greatest distance between its terminals.

The line begins in 15th arrondissement of Paris at the level of the Porte de Sèvres.
The rear station at Balard is under the Paris heliport, beyond the Boulevard Périphérique viaduct.
The station has three tracks and a central platform, with the end of the line supplemented by four parking tracks.

It then runs toward Hôtel des Invalides along Avenue Félix-Faure, passing under the Chemin de fer de Petite Ceintureviaduct and arriving at the Lourmel station (three tracks with platforms, one of which runs to the Javel maintenance workshop.
It then serves the Boucicaut and Félix Faure stations.

After these stations, Line 8 follows the Rue du Commerce.
Because of the narrowness of the street, the Commerce station has staggered platforms.
At the intersection of Rue du Commerce and Avenue Emile-Zola, the Line 8 tunnel is under Line 10 in a common structure.
As the line reaches the La Motte-Picquet – Grenelle station, the eastbound Lines 8 (toward Créteil – Préfecture) and 10 (toward Austerlitz) use the same central platform; the westbound Line 8 (toward Balard) is under the westbound Line 10 for historical reasons.

The line then follows Avenue de la Motte-Picquet at a .04-percent grade, bringing it near the surface.
The Champ de Mars station, between La Motte-Picquet – Grenelle and École Militaire, was closed on 2 September 1939.
A rush-hour track, unusual in the system, and a connection are between the La Motte-Picquet – Grenelle and Champ de Mars stations.

After the Champ de Mars ghost station the line serves École Militaire and La Tour-Maubourg, curving right and left under the Invalides esplanade and beginning a .04-percent descent under the park tracks and the main tracks of Line 13 to the Invalides station under the Rue de Constantine.
At Rue Robert-Esnault-Pelterie, it begins a second .04-percent descent under RER Line C to cross the Seine through a metal tunnel.
The line then goes up the Right Bank on a curved, .035-percent grade to the Concorde station.

Line 8 then runs under Rue Royale, under the Asnières sewage-treatment plant and then above Line 12, to reach Madeleine.
It crosses Line 14, passing the Clichy sewage-treatment plant to Opera before skirting the Grands Boulevards to Richelieu – Drouot.
At this station Lines 8 and 9 begin a common infrastructure, with Line 8 above Line 9.

Both lines reach the same level at République, via Grands Boulevards, Bonne Nouvelle, Strasbourg – Saint-Denis and the closed Saint Martin station.
On the east side of République the tunnel widens to three and then four tracks, used by both lines for connections on the west side of the station.

The line continues under the Grands Boulevards to Bastille, via Filles du Calvaire, Saint-Sébastien – Froissart and Chemin Vert.
Before arriving at Bastille, it descends under Line 5 and Canal Saint-Martin at a .40-percent grade.
The line then follows the Rue du Fauborg-Saint-Antoine to the Ledru-Rollin and Faidherbe – Chaligny stations, curving to follow the Rue de Reuilly to the Reuilly – Diderot station.

Line 8 reaches Montgallet on a .04-percent grade before the Bois de Vincennes, via the Daumesnil, Michel Bizot and Porte Dorée stations.
It then turns southwest to the Porte of Charenton station.
The line then turns southeast, leaving Paris to cross the commune of Charenton-le-Pont via the Liberté and Charenton – Écoles stations.
This station has two tracks with platforms and two sidings, since it was a longtime terminus.

The line continues in open air for 353 meters before crossing the A4 autoroute and the Marne.
The viaduct is two metal, 199-metre structures, with a slope of .04014 percent.
Line 8 goes underground again through Maisons-Alfort along Avenue Général-Leclerc, via the École Vétérinaire de Maisons-Alfort, Maisons-Alfort – Stade and Maisons-Alfort – Les Juilliottes stations.
The latter, a former terminus, has three tracks with
Line 8 is 22.057 km (13.706 mi) long, including 2.8 km (1.7 mi) of open-air tracks in the southeastern suburbs. It is the second-longest line (after Line 13), with the greatest distance between its terminals.
The line begins in 15th arrondissement of Paris at the level of the Porte de Sèvres. The rear station at Balard is under the Paris heliport, beyond the Boulevard Périphérique viaduct. The station has three tracks and a central platform, with the end of the line supplemented by four parking tracks.
It then runs toward Hôtel des Invalides along Avenue Félix-Faure, passing under the Chemin de fer de Petite Ceintureviaduct and arriving at the Lourmel station (three tracks with platforms, one of which runs to the Javel maintenance workshop. It then serves the Boucicaut and Félix Faure stations.
After these stations, Line 8 follows the Rue du Commerce. Because of the narrowness of the street, the Commerce station has staggered platforms. At the intersection of Rue du Commerce and Avenue Emile-Zola, the Line 8 tunnel is under Line 10 in a common structure. As the line reaches the La Motte-Picquet – Grenelle station, the eastbound Lines 8 (toward Créteil – Préfecture) and 10 (toward Austerlitz) use the same central platform; the westbound Line 8 (toward Balard) is under the westbound Line 10 for historical reasons.
The line then follows Avenue de la Motte-Picquet at a .04-percent grade, bringing it near the surface. The Champ de Mars station, between La Motte-Picquet – Grenelle and École Militaire, was closed on 2 September 1939. A rush-hour track, unusual in the system, and a connection are between the La Motte-Picquet – Grenelle and Champ de Mars stations.
After the Champ de Mars ghost station the line serves École Militaire and La Tour-Maubourg, curving right and left under the Invalides esplanade and beginning a .04-percent descent under the park tracks and the main tracks of Line 13 to the Invalides station under the Rue de Constantine. At Rue Robert-Esnault-Pelterie, it begins a second .04-percent descent under RER Line C to cross the Seine through a metal tunnel. The line then goes up the Right Bank on a curved, .035-percent grade to the Concorde station.
Line 8 then runs under Rue Royale, under the Asnières sewage-treatment plant and then above Line 12, to reach Madeleine. It crosses Line 14, passing the Clichy sewage-treatment plant to Opera before skirting the Grands Boulevards to Richelieu – Drouot. At this station Lines 8 and 9 begin a common infrastructure, with Line 8 above Line 9.
Both lines reach the same level at République, via Grands Boulevards, Bonne Nouvelle, Strasbourg – Saint-Denis and the closed Saint Martin station. On the east side of République the tunnel widens to three and then four tracks, used by both lines for connections on the west side of the station.
The line continues under the Grands Boulevards to Bastille, via Filles du Calvaire, Saint-Sébastien – Froissart and Chemin Vert. Before arriving at Bastille, it descends under Line 5 and Canal Saint-Martin at a .40-percent grade. The line then follows the Rue du Fauborg-Saint-Antoine to the Ledru-Rollin and Faidherbe – Chaligny stations, curving to follow the Rue de Reuilly to the Reuilly – Diderot station.
Line 8 reaches Montgallet on a .04-percent grade before the Bois de Vincennes, via the Daumesnil, Michel Bizot and Porte Dorée stations. It then turns southwest to the Porte of Charenton station. The line then turns southeast, leaving Paris to cross the commune of Charenton-le-Pont via the Liberté and Charenton – Écoles stations. This station has two tracks with platforms and two sidings, since it was a longtime terminus.
The line continues in open air for 353 meters before crossing the A4 autoroute and the Marne. The viaduct is two metal, 199-metre structures, with a slope of .04014 percent. Line 8 goes underground again through Maisons-Alfort along Avenue Général-Leclerc, via the École Vétérinaire de Maisons-Alfort, Maisons-Alfort – Stade and Maisons-Alfort – Les Juilliottes stations. The latter, a former terminus, has three tracks with 
Paris Métro Line 8