Havant-based recruitment company Jobsite.co.uk will be Pompey's main club sponsor for the next three years.
The online recruitment site Jobsite have signed a three year contract with the club, with the logo appearing on all first-team shirts, training wear and replica kit.
The club said the deal is in excess of their previous deal with OKI – which was 4m over three years.
As part of the agreement, the Fratton End will now be known as the Jobsite Stand.
Jobsite chief executive officer Keith Potts said: 'Portsmouth Football Club is closely aligned with our brand values; they're a down-to-earth, straight-talking, hard-working club who are renowned as having some of the best fans in football.
'They're also our local club and we're extremely proud that they're in the Premier League. We're excited to be their shirt sponsor and to be supporting them as the new season starts.'
Pompey chief executive officer Peter Storrie said: 'We're delighted to welcome Jobsite as our new main club sponsor.
'This represents the biggest sponsorship deal in the club's history.
'We have been impressed by Jobsite's attitude and approach to supporting the club and believe that they will be a great partner.
'Jobsite are joining at an exciting time for the club and we look forward to building a close working relationship with them.'
Paul Bell, Pompey's commercial director, added: 'From the initial conversation with Jobsite it was clear that they were serious about extending their brand awareness campaign into new ground to reach more consumers.
'Becoming the main sponsor at Portsmouth Football Club will help them to reach significant audiences both in the UK and worldwide.'
Pompey superfan John Westwood, said: 'I think it's fantastic. It shows that people have got confidence in the club and the new owners.
'It's another indication that the club is going places. It's the beginning of a new era.
'It's quite apt that they should be sponsoring us with the current economic climate. I think it's great all round.'
Nigel Tressider, chairman of the Portsmouth Supporters Club, added: 'I'm pleased we've got a three-year deal, and I'm just pleased we've got a sponsor really.
'The money going into the club will help.'
The club is yet to release any details about the launch date for the new kit.
PARTNERS IN HELPING PEOPLE FIND WORK
Pompey aren't the only ones teaming up with Jobsite.
The Havant-based company have recently struck a deal with Johnston Press, publisher of The News.
The News and Jobsite will work together as The News continues to advertise jobs locally in the Jobs Today section.
Jobsite is a locally-based company which launched back in 1995.
It was launched as the UK's first commercial multi-sector online recruitment site.
It is now one of the UK's best known online recruitment brands.
Nearly a million CVs are currently posted on the site for employers to search.
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