NEW YORK and PARIS—The merger of international marketing services companies Omicom and Publicis Groupe—expected to be formally announced later today— will create the largest holding of public relations businesses in the world, bringing together a roster that includes global brands including FleishmanHillard, Ketchum, MSLGroup and Porter Novelli, with a combined fee income in excess of $1.82 billion, based on numbers published as part of our Holmes Report 250 global ranking.

That’s enough for the merged business to overtake WPP, which reported public relations and public affairs fees of $1.49 billion for 2012.

The addition of MSLGroup to the Omnicom portfolio will also strengthen the group’s PR operations in the fast-growing Asia-Pacific region. While FleishmanHillard has established itself as a major player in the region over the past five years; Ketchum still lags most of its peers despite a number of acquisitions in recent years; and Porter Novelli is a minor force, except for its Shunya operation in China.

MSL, by contrast, has been on an acquisition binge in China and India, and was named our Asia-Pacific Consultancy of the Year just a few weeks ago.

MSLGroup also brings with it a serious capability in the high-end financial communications realm. It owns Kekst and Company, a perennial leader in the US mergers and acquisitions business, and international boutique CNC, as well as Publicis Consultants in Paris, JKL in the Nordics and Capital MS&L in the UK and the Middle East.

While Omnicom is a joint venture partner in Kreab Gavin Anderson, that firm rarely features among the leaders in the M&A rankings. The US-based holding company also owns Clark & Weinstock and Chlopak Schecter & Partners, both known for their public policy expertise. Public affairs is one area where MSL remains under-strength compared to many of its peers.

Other agencies in the Omnicom fold include cause branding and corporate responsibility specialist Cone and lifestyle and healthcare public relations firm Marina Maher Communications.

According to published reports, Publicis’ chairman and CEO Maurice Levy will be chairman of the merged company, with Omnicom’s John Wren (pictured) as CEO.