The pair complete Publicis' senior management line-up. Ewart replaces Nik Studzinski, who quit in February to join Mother, while Lear takes over from Kim Douglas, who left Publicis in November last year without a job to go to.
Neil Simpson, the Publicis chief executive, said: "I'm trying to build a new communications agency and want a senior management team with the experience, but also the hunger, to roll their sleeves up and build something new."
In 2007, Publicis lost the Post Office and Asda accounts, and is yet to replace the combined £56 million in billings. In the same year, Grant Duncan, its chief executive, and Tim Lindsay, the chairman, also left the agency.
Shop, formerly known as Campbell Doyle Dye, will officially close its doors at the end of May.
Last week, the agency parted company with Invesco, not long after it lost its flagship Mercedes-Benz business following a consolidation into BBDO.
None of the agency's other senior management team has a job lined up, although Casper Thykier, Shop's managing director, is in talks with Freud about replacing Tom Vick (see story page 3).
Shop launched as Campbell Doyle Dye in 2001 by the creatives Walter Campbell, Sean Doyle and Dave Dye. The start-up's management team also included Thykier and the former Lowe Lintas planning director Alison Hoad.
The agency won the £10 million Mercedes account soon afterwards and later created the acclaimed "lucky star" campaign.
Ewart has previously worked at Abbott Mead Vickers BBDO, while Lear joined Shop in 2005 from CHI & Partners.