Matthew Bell has left Ferrari Press Agency after 15 years as co-owner and co-director with Adam Gillham, to become acting night news editor at The Sun.
It means he has also stepped down with immediate effect as chairman of the National Association of Press Agencies (NAPA) after four years in that role.
Bell, 45, said: "I've worked really hard together with Adam to build up Ferrari's into one of the best news agencies in the UK. We've produced lots of great exclusive stories, as well as nurturing so many young reporters who have moved on to enjoy success in staff positions on national newspapers. We're both very proud of that.
"I'll always remain emotionally attached to Ferrari's but I felt it was time for a new challenge for me. I know the agency will continue to thrive with Adam at the helm of a team of talented reporters.
"I'm really looking forward to working at The Sun with another team of talented reporters, some of whom used to work at Ferrari's."
The agency, which covers Kent and south London, is named after former Mirror night editor Lino 'Dan' Ferrari, and is due to celebrate its 70th anniversary next year. Lino's son is Nick Ferrari, LBC broadcaster and TV commentator, who remains a supporter of the agency.