Keolis Downer is a joint venture between Keolis, the largest private sector French transport group, and Downer Rail, an Australian railway engineering company, that operates bus and tram services in Australia.

In June 2009, the Victorian government awarded to Keolis Downer the franchise to operate the Melbourne tram network in Melbourne, Australia^[1] for eight years, starting in November 2009.^[2][3] In September 2017, having substantially met performance criteria, the franchise was extended until 30 November 2024.^[4] Keolis Downer operates the Melbourne tram network under the Yarra Trams name, which had been used by the previous operator TransdevTSL.^[5][6][7]

In July 2014, Keolis Downer began operating the G:link tram operation on the Gold Coast.^[7][8] In March 2015, Keolis Downer purchased bus operator Australian Transit Enterprises, which operated the Hornibrook Bus Lines, LinkSA, Path Transit and SouthLink operations with 930 buses.^[9]

Keolis Downer, trading as Newcastle Transport took over the Newcastle Buses & Ferries operation in July 2017. It began operating the Newcastle Light Rail in February 2019.^[10][11][12]

In January 2021, Keolis Downer began an eight-year contract to operate the Adelaide Metro rail network.^[13][14][15]

In October 2021, Keolis Downer Northern Beaches began an eight-year contract to operate Region 8, the Northern Beaches and Lower North Shore, of the Sydney Metropolitan Bus Service Contracts.^[16] Keolis Downer has operated on-demand services in the area since November 2017.^[17][18]