The duo have been at Lowe for the past 18 months working on Vauxhall and Malvern Water. The move sees them reunited with Hastings, who hired them to work at D'Arcy when he was its creative head two years ago.
At D'Arcy, they created the social work campaign for COI Communications, which won a gold Lion at Cannes as well as a D&AD silver.
Hastings said: "I've always been a big fan of Justin and Christian. They're talented blokes and dead likeable with it. Citroen is a great opportunity for them I am sure they will bring the brand the kind of advertising it needs."
The copywriter Hooper and the art director Cotterill began their careers at HHCL & Partners in 1992, going on to spend two years in Hong Kong at DDB and Euro RSCG.
In 1994, they began a five- year stint at Ogilvy & Mather where, in addition to working on the Ford and Lucozade accounts, they became the first team to win a gold at Cannes for work on a Unilever account, with "art school" for the Impulse deodorant brand.
Cotterill said: "When Nick spoke to us, we jumped at the chance to work on a world-famous brand with a heritage such as Citroen's."
Hooper added: "We are looking forward to renewing our successful working relationship with Nick."