The agency’s retained brief comes ahead of the former IBF and WBA light-welterweight champion's fight against Mexico's Julio Diaz in Sheffield next Saturday (27 April).
It will be working to position Khan as a major sporting personality beyond the world of boxing and seek to develop his commercial potential.
Khan, who lost his WBA and IBF titles to Lamont Peterson in 2011, has two fights planned this year but this week told media the next bout may be his last in the UK as he chases the bigger fights in the US.
Tangerine’s appointment comes four months after poaching Mary Harding from M&C Saatchi Sport and Entertainment, which is understood to have parted ways with Khan last autumn.
Harding, MD of Tangerine PR’s consumer team, said: 'Prior to my recent move to Tangerine, I had been working with Amir and his team for a number of years. This collaboration sees Tangerine’s first move into talent PR and we are thrilled to begin this development of our offer with one of Britain’s best-known boxers.
‘We’re looking forward to helping him increase his profile across a range of sports and lifestyle media, building his brand and increase his commercial appeal.’
Khan, a four-time world champion, became Britain’s youngest boxing medallist at the 2004 Olympics in Athens by winning silver when aged just 17.