The move follows Leo Burnett Italy's appointment to the Lindt business in other European markets earlier this year.
Lindt, which previously handled its UK advertising in-house, last used an agency for UK campaigns in 2008. It parted company with Grey London, which had won the business a year earlier in a pitch against Leo Burnett.
Lindt, which spent £4.7 million on advertising in the past year, according to The Nielsen Company, recently signed the tennis player Roger Federer as its brand ambassador.
Federer has since featured in US-specific advertising, through Gotham Inc, which shows him walking past airport security with a tennis bag full of Lindor truffles.
In March, Lindt ran its first digital campaign in the UK to promote its chocolate Gold Bunny ahead of Easter. It was developed by Standout UK.