The news under pressure Byrne quit following a string of controversies was announced at a press conference on Monday following an emergency meeting of the Policing Board.
It comes after a row erupted last week when High Court judge Mr Justice Scoffield ruled that two junior officers were unlawfully disciplined for an arrest made at a Troubles commemoration event in 2021.
The judge said they had been disciplined to allay a threat that Sinn Fein could withdraw its support for policing. Sinn Fein has insisted there was no such threat.
At the press conference, Policing Board chair Deirdre Toner said Mr Byrne had tendered his resignation with immediate effect.
She said: “The chief constable Simon Byrne has today tendered his resignation to the Northern Ireland Policing Board with immediate effect.
“I have informed the board of the resignation at a special meeting this afternoon.
“I would like to record my thanks and appreciation to Simon for his work over the course of the last four years as chief constable.
“He is undoubtedly a dedicated police officer with a deep respect for the profession of policing.”
Mr Byrne was already facing pressure following a major data breach from the PSNI last month.
Personal data on all serving members of the PSNI was mistakenly published in response to a freedom of information request.
Details of around 10,000 PSNI officers and staff included the surname and first initial of every employee, their rank or grade, where they are based and the unit they work in.
The PSNI has confirmed the list is in the hands of dissident republicans, who continue to target officers.
A number of other data breaches has since come to light, including the loss of a police officer’s laptop and notebook which contained details of 42 officers and members of staff after the items fell from a moving vehicle.
Ms Toner said the board will now consider new leadership arrangements as she paid tribute to the outgoing chief constable.
She said: “He was very aware of and greatly appreciated the often difficult job that officers and staff across the organisation do on behalf of the community.
“This may not always have been apparent to onlookers but it was very much his modus operandi, as was his desire to improve policing for the community through modernisation and investment in local policing arrangements.
“His tenure was subjected to intense scrutiny and I am sure that the last few weeks in particular have been incredibly difficult for him personally and professionally.”
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