O'Flynn leaves his role as comms director having joined UKIP at the start of the year from the Daily Express, where he was chief political commentator.
In the new role he will share responsibility for the party's economic brief with Steven Woolfe, who will look after financial services.
Nigel Farage, UKIP leader, said O'Flynn would be "responsible for setting out our macroeconomic positions and honing our message on tax and spending issues".
O’Flynn, who was recently elected MEP for the East of England, said: "I am really looking forward to this new challenge of developing an economic message that is about promoting growth and enterprise on one hand, but also delivering fairness and restoring a sense of hope for millions of hard-working families who have seen their living standards plummet."
A UKIP spokesman said there was "nothing finalised" regarding replacing O'Flynn in the director of comms role.
Other changes to the UKIP front bench announced today include Diane James being made the party’s home affairs and justice spokesperson and Mike Hookem being appointed defence spokesman.
O’Flynn had been a Fleet Street political journalist for 18 years before joining UKIP, spending eight years as the chief political commentator for the Express.