The Arizona-based company, which is backed by Napster founder Sean Parker, holds an almost 50% share of the $300m (£186m) e-cigarette market in its home country.
In June it raised $75m for marketing and international expansion as well as clinical trials and R&D.
The brand's international marketing director Roger Harrison has appointed Hotwire to handle corporate PR in the UK and Western Europe and Seven Dials for consumer PR in the UK following pitches.
Hotwire's brief is to position NJoy's product as providing a credible alternative to smokers and manage its reputation within the e-cigarette industry. Work will be led by Hotwire associate director Laura MacDonald with support from its network of European offices at a local level.
Seven Dials' brief is to boost awareness of NJoy among UK consumers through creative PR ideas, media relations and celebrity and influencer campaigns. The agency's work will be led by associate director Dan Turner and business director Eleanor Conroy.