The firm, which is also the world's biggest direct seller of cosmetics, has awarded Halpern a UK and Europe-wide brief.
Avon reported global third-quarter profits of £78.6m, down 38 per cent on the same period last year.
Halpern's first task will be to promote ranges such as Mark, Avon Anew and Avon Advance Techniques to UK consumers in the run-up to Christmas, and to western, central and eastern Europeans in the new year.
Halpern Health & Beauty account director Fiona Hughes said the agency would look for high-profile brand ambassadors to give Avon greater presence in women's glossies. The agency will also provide press office support, she added.
Avon's product lines include brands Skin So Soft, Avon Colour and Today, Tomorrow, Always.
Avon has relied on its in-house team in recent years, but has used Capella Communications for breast cancer awareness campaigns (PRWeek, 17 June 2005).
Halpern reports to Natalie Deacon, head of PR for Avon UK, and Alex Long, executive director of European regional marketing.
There are more than 160,000 Avon ladies - now known as ‘representatives' - in the UK, making them a similar-sized group to the British Army. New reps pay a £15 joining fee, receive training and a selling guide in return, and can buy a starter pack with samples.
Avon produces a new brochure every three weeks, from which reps order stock. They earn up to 25 per cent commission.
In June, Julia Roberts signed a £2.2m-a-year contract to be the face of Avon.