Bigmouthmedia won the account after a competitive pitch and will run Cdiscount's SEO campaign.
The website, which is three-times larger than Amazon in its native France, will be looking to undercut the competition by up to 50% with a range of aggressive sales.
Arfan Sabir, online marketing manager at Cdiscount UK, said: "The credit crunch has created a real opportunity for online retailers.
"Value for money is what really matters to consumers right now, and our launch campaign will be led by a series of very strong offers designed to knock the existing big players off the radar.
"Bigmouthmedia's international reputation, together with their proven track record in the retail space, made them the natural choice of partner for the crucial opening phase of our launch in the UK."
Finlay Clark, senior retail strategist at bigmouthmedia, said: "If anything, the current economic climate has given fresh impetus to the online retail sector, and this promises to be an exciting campaign."