The collection includes baptism, banns, marriage and burial records from 14 Welsh counties, dating from the 16th to the 20th century.
However, Findmypast’s 10-year exclusivity deal has now expired, meaning other family history websites are free to add the records.
The parish records make it possible for family historians to comprehensively trace their Welsh roots beyond the introduction of civil registration in 1837.
The eight million records contain 14.5 million names.
Ancestry and TheGenealogist have added searchable indexes of the records accompanied by digital images of the original documents.
MyHeritage has added the indexes and will add the images at a later date.
Ancestry will also continue to work with the 12 participating archives, scanning new records that have been added since the project initially began.
Rhona Murray, content acquisition manager at Ancestry, said: “These records are an invaluable resource for anyone looking to research the history of Wales and its people and our ambition is to create the highest quality and most comprehensive Welsh Parish Register record collection online.”
Ancestry will work with Glamorgan, West Glamorgan, Gwent, Pembrokeshire, Anglesey, Denbighshire, Gwynedd, Powys, Carmarthenshire, Ceredigion, Conwy and Flintshire archive services.
Wrexham, the only other archives in Wales – does not hold original parish registers and their registers for their area are held in a neighbouring archive.
Ancestry has also been working with the archive community to improve the metadata of the collections.
This will make the collection more accessible by improving spelling of the parish names, providing more detailed variant names, ensuring all parishes are placed in the right county and allowing users to search for the Welsh and English names.
Hayden Burns, senior archivist at Anglesey Archives, said: “We are excited to work with Ancestry to widen the access to our online parish registers collection.
“We have been enthusiastically supporting their project to enhance the parish place data and hope this will support the people of Wales and the Welsh Diaspora to trace their roots with ease.”