Warner Music has signed a deal with media site 7digital.com to offer its music without copy protection.
Customers in the UK, Ireland, Spain, France and Germany will be able to download albums by artists such as Madonna and the Red Hot Chilli Peppers.
The MP3 files can be played on nearly all music devices including Apple's best selling iPod.
7digital.com is the first European site to offer Warner's music free of Digital Rights Management (DRM) systems.
The label had previously signed a deal with Amazon to sell its tracks in MP3 format. The service is currently only available in the US although this is expected to change later this year.
The music download market is dominated by Apple's iTunes, which sells most of its music in a proprietary format that can only be played on Apple devices such as the iPod.
Users can copy downloaded songs to a CD and then copy the disc back on to the computer so that the songs can then be moved to other portable devices - but the quality of the music is affected.
The firm has also experimented with DRM-free music services. Last year it launched its premium rate iTunes Plus service, but it currently only offers EMI tracks.
7Digital.com also offers EMI music, and is reportedly in discussions with Sony BMG and Universal.
If it secured those deals it would boast all of the big four music labels and could offer a credible competitor to Apple's service.
James Bates of research firm Deloitte called the deal "significant".
"Today's announcement may be a tipping point in the general move to DRM-free data," he said.