In an online announcement today Demotix said Corbis "is acquiring the whole company to better integrate us into their global news operation".
In March last year Demotix and Corbis signed a partnership which saw Corbis able to select Demotix images which would then be distributed through its website.
Today Demotix said its acquisition is "an enormous step towards our goal of becoming a truly competitive international photojournalism agency".
"Corbis have been extremely supportive partners over the last 18 months, and the results of our collaboration are plain for all to see: doubling our contributor base, doubling our image and video ingest, and multiplying sales many times over," chief executive Turi Munthe said in the announcement.
Speaking to Journalism.co.uk he said the platform has "proved the model with pictures, now we will drive hard towards video, assignments, audio and a few other core areas of growth".
"Corbis is the perfect home for us and our network of contributors to really expand."
In the online post Munthe added said that while "there will surely be changes" during the integration, Demotix's "core team will stay the same".
In a press release Corbis chief executive Gary Shenk added: "Today's announcement underscores our commitment to providing our media customers access to an exceptional selection of breaking news imagery -- from premium news sources to alternative coverage outside of the scope of the mainstream newswires."
"Demotix helps build out Corbis' unmatched portfolio of news and entertainment imagery that cannot be found anywhere else."
According to a press release terms of the acquisition have not been disclosed.