Ki-moon dedicated the light sculpture on top of the new wing of the BBC Broadcasting House building to the memory of journalists and news staff killed while upholding freedom of speech.
The memorial sculpture, titled Breathing, is a 10m-high glass and steel construction shaped like a giant listening glass.
It will project a beam of light up to one kilometre into the sky at 10pm every night for 30 minutes, in tandem with the BBC's news bulletin.
Last night's inauguration, co-hosted by the International News Safety Institute and the BBC, follows the recent deaths of two BBC journalists in Afghanistan and Somalia -- Abdul Samad Rohani and Nasteh Dahir Faraah.
Rodney Pinder, director of INSI, said: "These men and women are the unsung heroes of democracy, for without a free press there can be no freedom.
"This shaft of light in the capital of international journalism is a visual reminder of their sacrifice."
An INSI study issued in March last year, found that every week, for the past ten years, at least two journalists or news staff have been killed trying to report the news and in 90% of cases no-one is brought to justice.
Mark Thompson, BBC director-general, said: "We should never forget or underestimate the risks that journalists reporting from hostile environments face.
"We hope this poignant memorial will serve as a nightly reminder of the sacrifice made by many in the cause of free expression and journalism."
The light sculpture was formed through a collaboration between artist Jaume Plensa, the Broadcasting House architect Sir Richard MacCormac and his team from MJP Architects, public art consultants Modus Operandi and engineers Whitby Bird & Partners.
The BBC also commissioned a poem by ex-war correspondent and poet James Fenton, entitled 'Memorial'.
The poem remembers the bravery and self-sacrifice made by news journalists and their crews from news organisations across the world.
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