Omnicom and IPG sent shockwaves through the advertising sector when they announced a $13bn merger on Monday. Ali Lyon looks at what the deal means for the firms’ agencies, staff and the ad industry as a whole.

Advertising, according to Mad Men’s Don Draper, is based on one thing: happiness.

Happiness, the protagonist of the HBO hit series says, “is the smell of a new car”. It’s “a billboard on the side of a road that screams with reassurance that whatever you’re doing is OK”. It’s “freedom from fear”.

The sector has come a long way from the flared suits, physical flip charts and outdated gender roles that punctuate the popular drama set in high-octane 1960s New York.

But the top brass at two advertising giants of today – Omnicom and Interpublic Group (IPG) – will be working in overdrive currently to ensure their own staff retain the “freedom of fear” to which Draper alludes.

The pair of holding groups revealed on Monday a deal that threatens to uproot and reshape much of the contemporary advertising industry. The all-share $13bn mega-merger will replace IPG shareholders’ stock with Omnicom shares at a 21.5 per cent premium, in a tie up set to make the combined company the largest advertising, media and public relations group in the world.

The news set Adland ablaze with speculation on what the deal said about the state of the world’s $1 trillion (£784bn) ad sector, as well as its ramifications for the dozens of agencies sewed up in the sale.

It also sent jitters through the tens of thousands of UK staff that the New York-listed holding companies employ, many of whom read the press release trumpeting “annual cost synergies of $750m” and thought one thing.