It is Samsung's equivalent of Apple's Siri and Google's Assistant - which is pre-installed already in Samsung phones as they run the Android operating system.
Bixby will initially be available in only two languages - US English and South Korean.
The launch had been delayed since April.
Samsung did not give a reason at the time but early testers of a limited demo model - including the BBC - had reported that it failed to understand commands.
The firm's latest device, the Galaxy Note 8, is due to be launched on 23 August.
What makes Bixby different from other voice assistants is that it is deeply integrated with functionalities unique to Samsung devices, said Ian Fogg, analyst at IHS Markit.
"Samsung always differentiates its phones by adding a lot of its own features to Android," he said.
These include tailored support for its own hardware such as the curved edge screen, stylus, VR support and camera.
Mr Fogg added that over time Bixby could also be included in other Samsung products which do not run on the Android operating system.
"A lot of people believe one voice agent will become the sole agent everyone will use," he said of the rivalry among the tech giants over digital assistants.
"But in life we don't have one single expert that we trust for everything. It might be they are good at different things.
"For the user it's just as easy to say Alexa, or Cortana, or Siri - there is no barrier to choosing an alternative voice agent."
However, he added that the technology will only be successful if it is dependable.
"To make it work you have to be able to understand speech reliably. If you don't do that nothing else happens. That should be a given".
Samsung's voice-controlled digital assistant Bixby is being rolled out in 200 countries from today.