Google's product portfolio includes email service Gmail, the smartphone Pixel (pictured above) and video-sharing site YouTube, among many others.
The company has already conducted creds meetings with a number of PR agencies. Successful firms are expected to start pitching for the business later this month, it is understood.
According to a Google spokesperson, the company is "always speaking" with different agencies, but declined to comment further.
Incumbent Portland also declined to comment.
Google also works with Ogilvy PR on a project basis, but this is not expected to change.
The tech behemoth, which is headquartered in California, was founded in 1998 by Larry Page and Sergey Brin and recorded revenues of $74.54bn (£60.7bn) in 2015.