The agency won the business after going up against Crossing O'Sullivan, The Bottom Line and Claydon Heeley.
Beatthatquote.com previously worked with Muir Howard, which launched a direct response TV campaign for the site last year, but it is thought that the agency did not repitch for the account.
John Paleomylites launched the Beatthatquote.com brand in 2005 offering users the chance to search for and compare quotes and rates on a range of financial products. Its main competitors are moneysupermarket.com, comparethemarket.com and gocompare.com.
Earlier this year it was named the fastest growing website of 2007 according to Nielsen Online data.
Beatthatquote.com increased its UK audience by 1,165% to 392,000 users last year, beating Facebook's 781% audience growth in the UK, and taking the price comparison site's total users to 8.9m from 1.1m in 2006.
The first campaign from Leagas Delaney is set to launch on TV, outdoor, press and online on August 25.
Elliott Moss, managing director at Leagas Delaney, said: "Our challenge is to establish Beatthatquote.com - a brand with a unique service offering and a strong entrepreneurial ethos - as the first genuine brand in what is still a very immature market.
"The online price comparison marketplace is growing exponentially at the moment - but even people who have used one of these websites don't have any kind of relationship with or loyalty to the players which currently dominate the category."
Paleomylites, Beatthatquote.com managing director, said: "Beatthatquote is a young, aggressive, ambitious company. We needed to find an agency partner who would bring to life our offering in an impactful and differentiating way. Leagas Delaney really impressed us."
In February Beatthatquote.com appointed M2M to handle its offline media planning and buying account leaving its online media planning and buying with All Response Media. However, two months later it moved the offline work back to All Response Media.