Documents such as medal and grave records, census information, family photographs and battalion diary entries record their lives, but the IWM says it is still seeking more details about them.
The project, which is free to use, is being supported by DC Thomson Family History, which runs several online ancestry websites.
Each person in the archive will have their own web page, where the public can upload photographs, write stories and recollections or add links to other records.
The IWM says the centenary of WW1 will see many families showing a renewed interest in documents, diaries, letters or photographs handed down by relatives or picked up from museums, libraries and archives.