An unused Flinders Street Station train line has been given a new lease of life as Melbourne's longest bar.

Located next to Flinders Street's Platform 13, a train line first used by Australia's steam railway has been transformed into the Arbory Bar and Eatery, stretching 120 metres along the Yarra.

Open each day from 7.30am until late, the new bar and restaurant has a breakfast menu, an all-day menu, and a late-night menu catering for the after-dark crowd.

The site replaces the abandoned Sandridge train line that used to run to Port Melbourne but was closed almost three decades ago.

The Arbory was the product of a joint venture between HQ Group (responsible for Coffee HQ) and Metro Trains. Planning for the new eatery started four years ago.

The venue, which features a large wooden deck and illuminated shipping containers, was designed by Jackson Clements Burrows Architects and connects with the Princes Bridge and Southbank footbridge.

Head chef Nicholas Bennett hails from Trocadero (now Fatto) and Michelin-starred British restaurant Tom Aikens Restaurant.

Metro Trains senior business development manager Mike Luxton has previously said the project was part of Metro's goal of "bringing stations to life".

"Through clever design, it will utilise a prime site within the Flinders Street Station precinct and become a vibrant area that many Melburnians will be able to enjoy."