The move follows the clearing by the Competition Commission (CC) of the merger of Global Radio and RSL, formerly GMG Radio, in London and West Midlands in May. The CC blocked the merger in seven other markets.
The main Smooth programming team is currently based in Manchester but the national station will broadcast from London from October.
A spokeswoman for Global Radio said: "Global Radio has today confirmed that the Smooth brand and its programming team will relocate to Global's headquarters in Leicester Square by the beginning of October.
"The RSL Direct sales team will also relocate to Leicester Square and to the new Global broadcast centre in Birmingham by October. Remaining areas of business will continue to operate under hold separate."
The spokeswoman declined to comment on how many people work in direct sales at RSL in the West Midlands and London, how many people work in the Smooth programming team or how many people RSL employs in the two regions in total.
Global Radio bought GMG Radio in June last year but although the deal was cleared on the grounds of plurality, the CC found it could lead to higher prices for advertisers in seven out of nine markets.