The network consists of WE, The Garrigan Lyman Group (GLG), Salt Branding, YouGov, Interel and Envy Create. Further partners may also join in the future.
It is being launched initially as an alliance, with leaders from the six members likely to meet on a quarterly basis, in addition to staffers working together more frequently to service mutual clients.
Clients listed on the network's website include major WE client Microsoft, as well as Renault, Skype, 3m, Nissan, Intel and international NGO the Forest Stewardship Council.
WE has also created a legal entity in the US, which it may choose to use as a formal vehicle for the alliance's work, depending on how it develops.
WE has worked with digital marketers GLG, branding firm Salt and market research company YouGov for some time. Its partnerships with public affairs network Interel and experiential marketing agency Envy Create are newer.
A WE announcement called Plus an "alternative to the increasingly bureaucratic and investor-focused holding companies and agency monoliths", with the agency's international president Alan VanderMolen saying: "We want to put the client first in a highly specialised network of independent agencies as an alternative to what we see as an increasingly homogenous offering from the holding companies."
The network has launched with a video showing how it intends to differentiate itself from other agency models.
The network's member agencies have combined billings in excess of $300m globally, and operate in 65 countries.
YouGov and Envy are based in London, Interel in Brussels, Salt in San Francisco and GLG in WE's hometown of Seattle.
After years of decline, WE grew its revenues by three per cent globally last year to become the 22nd largest PR firm in the globe, and one of the largest independent agencies, according to the new PRWeek Global Agency Business Report.