His appointment has been seen as a move to restore the media company’s reputation after the phone-hacking scandal and ongoing Leveson Inquiry.
Harri starts today and reports to chief executive Tom Mockridge. He will lead ongoing media management and provide the News International board with strategic reputational guidance.
Mockridge said: 'Guto is well qualified to lead us through the challenges we face as News International continues to change and progress.’
Harri said of his appointment: ‘News International has some of the most respected journalists in the UK, produces the most popular newspaper and has set itself the task of being the best governed media organisation in the future.
‘These are challenging times for the print industry in general and News International in particular. But with a proud heritage and firm commitment to serious journalism in print and online, I relish the chance to play my part in helping the new leadership secure a strong future.'
Harri replaces Andrew Honnor, who held the position in an interim capacity and has recently set up his own agency.
PRWeek reported that Harri had left City Hall on 8 May, stating that he had received an offer from News International.
Harri spent 18 years as a journalist before a brief stint in PR and four years as director of external affairs and spokesman for the Mayor of London. He left City Hall after helping to secure the re-election of Boris Johnson for a second term.