He is chair of REA Group,[1] a multibillion-dollar global digital advertising real estate company operated by News Corporation.

At the same time, it claimed a number of Cannes Grand Prix awards and built a market-leading digital practice upon their new client Telstra – Australia's largest telecommunications carrier.

[11] Under his leadership, the firm won global clients like LG, Bacardi, Dell, Goldman Sachs and Virgin Atlantic.

In March 2013 McLennan was appointed as CEO and managing director of Ten Network Holdings, replacing James Warburton.

[12] McLennan reshaped the audience strategy and revitalized the network's fortunes by implementing new sports and reality TV programming.

He also serves on the board of the Advertising Council, an American non-profit organization that creates and promotes public service announcements.

[26] In 2007, he invited former US vice president Al Gore to the Cannes Lions International Festival of Creativity to rally the industry in the fight against climate change.

[27] That same year, Y&R helped Gore build awareness of climate change through the Live Earth Concerts that took place on 7 continents on 7 July 2007.

McLennan has been a participant at the World Economic Forum in Davos, Switzerland, where he has served on panels, ranging from the future of the automotive industry to innovation.