Ryan joined financial PR consultancy Corfin Communications last October but has now set up RLF Partnership with Le Fevre.
He said he was taking a number of public and private sector accounts with him, but declined to name them.
Corfin was set up by Brunswick associate partner Harry Chathli and veteran financial journalist Neil Thapar in July last year.
'Joy and I have been talking about launching our own agency for years. We saw an increasing demand in the market for senior counsel, which made now the right time,' said Ryan.
The pair met when Ryan was comms director at retail bank TSB, where he retained Le Fevre Communications for two years from 1990.
Le Fevre brings 25 years of experience to RLF. She founded Le Fevre Communications in 1990 and sold her agency to The Media Square Group in 2003. She became CEO of the group's marketing agency Banc, stepping down last year to take a career break.
Ryan previously handled comms for Mars and BAE Systems, and has been a partner at Brunswick and a director at Edelman.
RLF is to operate from offices in Westminster from 1 July.