Construction of the 25-km light rail line will not begin until 2015, one year after it was supposed to be up and running.
It has now emerged that the Government will make a final decision on whether to proceed with the multi-billion euro capital project next year.
The project aims to link Tallaght with Dublin Airport.
Details of the delay were given at a briefing of Tallaght-based councillors on the status of the capital project.
The Metro West project was unveiled as part of Transport 21 and had a completion date of 2014, but the economic downturn has led to a number of capital projects being "parked".
A spokesperson for the Railway Procurement Agency (RPA) confirmed that Dublin's Metro North and Dart underground would be prioritised over the Metro West.
"Given the recent economic circumstances, the level of funding required for this project, along with the other large projects, is not available within the same time period and thus the completion date for Metro West has been delayed.
"Minister Dempsey has said that priority will be given to the Metro North and Dart underground and that the other projects should proceed through the planning and design processes."
Tallaght Mayor Mick Duff described the decision from the RPA and the Department of Transport as a "blow".
"Other capital programmes are being parked for the moment so it didn't come as a surprise to hear that we'll be waiting until 2019 for Metro West," he said.
The news comes just weeks after it was revealed that the Metro North will not be operational until 2016 and the Dart Underground in 2018. Both, if completed, will come on stream three years after they were originally due to start.
Metro West will provide a light rail system, similar to the existing Luas services, which will service Tallaght, Clondalkin, Lucan and Blanchardstown before it links up with the Metro North line at Dublin Airport.