Google Play Music already has a subscription-based service, where users pay monthly to listen to an unlimited amount of tracks.
The free version will be made up of curated playlists designed for different times of the day and tailored towards what you are doing.
The new free service, initially only available in the US, will include adverts similar to the Spotify model.
It uses Songza, an internet radio app that Google bought a year ago.
In a blog post, Google product manager Elias Roman said: "Even if you're not already a Google Play Music subscriber, we've got you covered.
"Google Play Music now has a free, ad-supported version in the US, giving you a new way to find just the right music - and giving artists another way to earn revenue.
"The new free, ad-supported version of Google Play Music is launching first in the US. It's available on the web today, and is rolling out this week to Android and iOS."
Google said it hopes the new free version will encourage people to sign up for the subscription-based tier of the service, which costs $10 (£6.34).
The service had around 815,000 paying subscribers in the US last December.
For now, Google isn't announcing any expansion of the free tier outside the US, though the paid plan is now available in 52 countries.
It'll compete against Apple's much-publicised new music service, which is due to launch on Tuesday 30 June and will be free for the first three months.
Earlier this week, Taylor Swift wrote an open letter to Apple over their plans to not pay artists during the 90-day Apple Music trial.
It led to the company reversing its stance and it now says it'll pay royalties for streams during that time.
Spotify announced last month that it would be offering video content for the first time and the world's second largest streaming site, Deezer, announced is adding more than 20,000 new podcasts to its service.
On Tuesday Peter Tonstad, the boss of the Jay Z's music streaming service Tidal, left the company after three months in the job.