The multi-million pound deal has been approved by the Radio Authority and will represent the news group's first sortie into radio.
Roger Parry, a co-founder and director of LNR, said he was 'delighted' with the outcome of negotiations which have stretched back to the early part of the year.
'It allows us to carry out to the letter the promise we made to the Radio Authority when we were awarded the London franchise last year.'
Describing Reuters as the 'dream shareholder', Mr Parry said the deal would bring the 'finance, resources and intellectual vigour' necessary to deliver LNR's planned rolling news service.
There was surprise last year when LBC lost its franchise to LNR, a group backed by merchant banker Guinness Mahon, and chaired by John Tusa, the newsreader and former head of the BBC World Service.
Although LBC was not due to come off air until October, Britain's oldest commercial station finally succumbed to the financial problems that had dogged its 21-year history and went into liquidation in March. Fearing that the capital's airwaves would fall silent, LNR bought LBC from the receivers last month.
LBC's two stations, Newstalk and Talkback, were to have been replaced by LNR's London First and London Extra. Mr Parry said the deal with Reuters would 'potentially have no impact on the station', addding that the news group had been 'impressed' with the programming LNR was planning.
The FM wavelength will carry a 'clock radio' service with regular news bulletins, while AM broadcasts will be based on phone-ins, not unlike LBC's Talkback.
John Parcell, managing director of Reuters (UK and Ireland), said: 'These local radio licences will be a showcase for Reuters' news services. The potential for audience growth - at a time when the radio advertising market is also growing - is tremendous.'
The sale has been approved by the Radio Authority and was welcomed at LBC, where around 80 staff are hoping it will secure jobs. A spokesman said: 'The place is buzzing. The feeling is that employees' positions are even more safe with this purchase. There is now a company with a lot of money behind it which will tide us over any difficult times.'
There has been speculation that LNR was struggling to produce a schedule that would meet its franchise obligations. Last month, Bruce Fireman was replaced as managing director.Reuse content