Construction work began in March 2001 on the Tallaght to Connolly line, as well as the Sandyford to St. Stephen's Green section of the second line, with
Ansaldo of Italy and MVM of Australia getting the contract to build the system. The St. Stephen's Green to Dublin Airport section was dropped before construction began, as it was decided to serve the area by a
metro instead. The contract to maintain operate the system was awarded to Transdev Ireland (formerly known as Connex). The extension from Connolly to The Point opened in 2009, with the extension from Belgard to Saggart opening in 2011. Interchange with the Green Line began in December 2017 with its extension crossing the Red Line either side of the Abbey Street stop. For three months in 2025, the line was curtailed following a fire at
George's Dock. The fire, on 18 August, damaged the bridge at George's Dock, and northbound services had to terminate at
Connolly station. The line fully reopened on 28 November 2025. ==Rolling stock==