McGinn has been acting editor of the free weekly magazine since September, when she took over duties from the former editor-in-chief Tim Arthur.
Arthur is now chief executive of the Time Out Group, which owns the brand in cities across the world. He was also initially promoted in an acting capacity after the previous chief executive, Aksel van der Wal, stepped down.
McGinn joined Time Out London in 2007. She will now oversee all editorial content in London across digital and print. The magazine launched a free iPad edition in July 2012 and relaunched as a free title that September.
She said: "I'm honoured to be taking on the editorship of Time Out London at such an exciting time for our flagship London magazine, our website and our global company.
"I was proud to play an integral role in the relaunch of Time Out's London magazine as a free title last year and look forward to building on our successes. Last month, we reached a record six million unique users online and our 500,000-plus print readership now makes us the most-read magazine in London.'
Time Out London was founded in 1968 and the brand now spans 37 cities across 25 countries.