Terms of the deal, including the size of WE's stake, were not disclosed.
WE Communications has around 20 staff around offices in Delhi, Mumbai and Bengaluru - these teams will be merged into the more than 150 staff of Avian.
Avian's sister public affairs business Chase remains a separate consultancy, owned by Avian WE and retains its name. Chase will continue to be led by Manash Neog.
The Indian investment comes almost exactly 12 months after WE, formerly Waggener Edstrom, announced the dual acquisition of Singapore-based WATATAWA and Shanghai-based Red Bridge.
In May last year WE set up the PLUS Network, now known simply as PLUS, bringing together a number of firms with complementary offerings.
Alan VanderMolen, WE president of international, said PLUS "helps us and our partners compete for the bigger briefs" and claims it is performing 100 per cent ahead of expectations in its first year, and that WE's international business has grown by 20 per cent organically this year.
Commenting on the acquisitons, he said: "We are in a great position to serve multi-market clients better than we ever have. These additions to our family are yet another example of WE aggressively expanding our global network in order to service a growing, global client base."
Avian Media was founded in 2004 by executive chair Nikhil Khanna, and is headquartered in Delhi with offices in four other cities. Claiming to be India's second-largest independent agency, clients include Airbnb, Airbus, Bloomberg, Dell, MasterCard, Qualcomm, Sony and TripAdvisor.
Khanna and his co-managing partner Nitin Mantri, who is the president-elect of ICCO, will continue to run the combined business.
Mantri said: "The merger between Avian into WE represents a huge opportunity for us to accelerate our expansion into new sectors and markets within the region. With the increased scale of the combined business, we can deepen our specialist capabilities, particularly in the areas of our power sectors technology, health and consumer, and provide our team with greater development opportunities."
WE veteran Carolyn Camoens will continue as WE's senior vice president of Southeast Asia, based in Mumbai.