The George's Dock Bridge, which was damaged in a fire earlier this month has to be demolished and rebuilt, causing delays to passengers on the Luas Red Line until the end of November.
Operator Transdev said an assessment has found that the bridge has been "structurally compromised" following the fire on 21 August.
"The existing bridge will need to be demolished, and a new bridge constructed," it said.
The operator said a programme for a replacement bridge has been developed, with completion of the works not due until November.
Luas Red Line services will remain suspended between Connolly and The Point until that time.
A replacement bus service will operate from tomorrow, covering the affected section of the line.
The service will run every 10 minutes and will operate during Luas operating hours.
Transdev said buses will be wheelchair accessible on the lower deck, with valid Luas tickets and TFI Leap Cards required to travel.
Luas staff will be on site to assist passengers throughout the disruption.
To facilitate the demolition of the bridge, changes to the overhead power cables will be required.
This will require a curtailment of Luas services on Tuesday and Wednesday from 7pm on both days.
After 7pm services will only run from Saggart and Tallaght to Smithfield. Morning services are unaffected.
During these specific shutdowns Luas customers tickets are valid on Dublin Bus.
Regular updates on the bridge replacement will be provided via the official Luas website and social media channels.
"We thank all passengers for their patience and cooperation during this period," Transdev added.
