Its network consists of eight offices scattered in cities across the UK.
While the structure of the agency, bought by Lord Chadlington's Huntsworth Group in August 2001, has helped HC conduct successful campaigns for the likes of Camelot (an account it recently relinquished after ten years) and Land Rover, getting disparate groups to work together requires constant, enormous effort.
And while having too few branches means an agency cannot do its job properly, having too many ceases to be cost-effective. 'There comes a point - we think we're at it - where to go further would be counter-productive,' says Kelly, who as deputy chairman took over the chief executive role from David Heal (who remains chairman) in August last year.
Kelly, 41, describes himself as an 'eclectic thinker' able to 'make lateral connections', and 'difficult to get riled'. He has built his expertise in organising people over his 12 years at HC, which he joined as head of the Southampton office at the then Saatchi & Saatchi-owned Hall Harrison Cowley. He then took on additional responsibility for Bristol and later the London office of what became HC after Heal's 1994 management buyout.
Graduating in politics and economics in 1983 from Leicester University, Kelly started in PR as a junior account executive at the then Profile Public Relations, then moved to Bovis as a PRO and, in 1986, went to Weber Shandwick as an account executive.
His most influential job, though, was as an account manager for Charles Barker chief executive Angela Heylin, who recruited him in the same year.
'You always got the feeling that people in the company were involved no matter what rank they were. I've tried to put some of that culture into HC,' Kelly says.
'We've all grown up since becoming part of Huntsworth. Chadlington is truly motivational, understands his business better than most and has an extraordinary vision for Huntsworth - and we've now found our place in that. That needs to be communicated to clients and staff and it's one of my big tasks: that everybody sees what we're trying to achieve and where we're going,' he adds.
HC began a major push into what it calls 'sports sponsorship exploitation' last month. The sports PR group is led by Edinburgh office associate director David Southern. The agency made its first foray into this territory last July, when it organised the launch press event for Scotch whisky brand Whyte and Mackay's sponsorship of Leeds United Football Club.
'We can do this for national clients regionally,' says Kelly. 'If you were going to do sports sponsorship and wanted to make sure it was really permeating down to the grassroots, we believe we have unrivalled capacity to deliver that.' Sports sponsorship PR is, he says, 'the way I see we're going to grow ourselves organically'.
When he does have free time, Kelly, who says he is competitive to the point of racing his two sons to finish breakfast, likes to fish near his home in Wimborne, Dorset, and go walking in the New Forest. Having played guitar in two school punk bands as a teenager, he still plays folk and rock for himself: 'All of it badly,' he says modestly.
So what of his peers? 'I think Paul is a class act,' says public affairs agency PPS founder and chief executive Stephen Byfield. 'He always seemed to be the driving force of HC behind the scenes, making things work. In the last year he has moved to centre stage. He has the vision and the detailed understanding to ensure delivery - a great all-rounder.'
Chadlington describes Kelly as a realist, something he believes is rare in the business. 'He is very capable of weighing the good and bad arguments and normally achieves a little bit more than expected,' he says.
'Also, there is no ego getting between him and the business. (For Paul) it's about building and leading a team of senior managers. That's why I think the company's going to continue to do very well,' he adds.
1984: Junior account executive, Profile Public Relations
1985: PRO, Bovis
1986: Account executive, Weber Shandwick
1986: Account manager, Charles Barker
1989: Associate director, HRA Design and Public Relations
1992: Southampton office MD, rising to chief executive, Harrison Cowley