Leventhal was MD at Eulogy before moving to Ogilvy PR 18 months ago.
The MD position did not exist at Spider prior to Levanthal's appointment, but was occupied by Richard Medley until February 2012 before he moved to Nexus.
Consumer and corporate PR shop Spider represents clients including Tyrrells Crisps, Maldon Salt, Kellogg's, Saga and FedEx.
The agency is based in London and employs 35 people. It was founded by former journalist Sara Pearson in 1990.
Pearson, who remains CEO of the agency, said: "Lara arrives at a time of strong business performance at Spider. Over the past two years we’ve achieved 30 per cent year-on-year growth across both consumer and corporate and with Lara’s dynamism and team leadership skills we're projecting similar growth in the year ahead. I’ve known Lara for a good few years and our collaboration has been an ongoing discussion."