Paris Métro Line 1 (French: Ligne 1 du métro de Paris) is one of the sixteen lines of the Paris Métro. It connects La Défense–Grande Arche in the northwest and Château de Vincennes in the southeast. With a length of 16.5 km (10.3 mi), it constitutes an important east–west transportation route within the City of Paris. Excluding RER (French: Réseau Express Régional) commuter lines, it is the most utilised line on the network with 181.2 million travellers in 2017 or 496,000 people per day on average.

The line was the network's first to open, with its inaugural section entering service in 1900. It is also the network's first line to be converted from manually driven operation to fully automated operation. Conversion, which commenced in 2007 and was completed in 2011, included new rolling stock (MP 05) and laying of platform edge doors in all stations. The first eight MP 05 trains (501 through 508) went into passenger service on 3 November 2011, allowing the accelerated transfer of the existing MP 89 CC stock to Line 4; however, as of 2019, Line 4 is also being converted to automated operations. The conversion allowed Line 1 to operate as the system's second fully automated line, after Line 14.

A transition to fully automated services was done without major interruption to passenger traffic. The new MP 05 rolling stock was able to operate efficiently alongside the manually-driven MP 89 CC rolling stock until there were enough MP 05 to no longer facilitate the need of the MP 89. Full automation was achieved for evening services in May 2012, with an increase to weekend services by August 2012. As of 15 December 2012, Line 1 is fully automated. The remaining five MP 89 CC trains remained stored on Line 1 near the Fontenay workshops until a new garage for Line 4 was opened south of the new Mairie de Montrouge station in February 2013.