The agency has been appointed following a four-way pitch organised by director of communications Mark Oakes (PRWeek, 9 August).
The register is seen as vital in improving the reputation and public confidence of the profession, as those signing up must adhere to a strict code of conduct.
There are an estimated one million care workers in the UK who must pay an as yet undisclosed fee if they want to register. Oakes said: 'It's important there is a focus on seeing those who register as customers. We want to keep them on the register and to do that we are looking into benefit packages.'
The agency has also been hired to work on a separate project to develop a three-year strategy for the body.
The H&K team is headed by senior associate director, corporate and business, Suzanne Prance.
The body, created by the Care Standards Act 2000 and headed by chairman Rodney Brooke is also due to start a recruitment drive as it seeks to strengthen its in-house team.
Nine extra staff, including a PA manager to head media, stakeholder and government relations, as well as being Oakes' deputy, are being sought to bring the team to 11.
The account win for H&K consolidates work it is already doing in the field of social work regulation.
Last week it was appointed to handle PR for the National Care Standards Commission, the watchdog that monitors care facilities and homes (PRWeek, 20 September).
Work being undertaken by the agency includes regional campaigning to promote reports on around 40,000 care facilities across England and the commission's online register, which is currently under development.
The NCSC was also created under the Care Standards Act.