The 54-year-old career civil servant will replace Stephen O'Brien, who held the post for two years, serving in what is widely viewed as one of the UN's most demanding jobs.
Lowcock's appointment comes as the United Nations faces the largest humanitarian crisis in its history with mass famine looming in four countries and donor funding falling far short of needs.
Guterres will announce the appointment of the new under- secretary general for humanitarian affairs and emergency relief coordinator on Friday, diplomats and UN sources told AFP.
He will be tasked with leading the UN's struggling relief efforts in Syria along with major aid operations in South Sudan, Yemen, Iraq, the Central African Republic and the Lake Chad region.
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The United Nations has appealed for $4.4 billion to help avert mass famine in South Sudan, northeast Nigeria, Somalia and Yemen. However, so far only $1.3 billion -- less than a third -- has been raised.
Lowcock will be the fourth British national to hold the leading UN post since 2007 after British Prime Minister Teresa May strongly backed his candidacy, UN sources said.
Lowcock is the first UN aid chief appointed by Guterres, who took over from Ban Ki-moon in January with a promise to overhaul the United Nations to improve its response to global crises.
O'Brien, a former British lawmaker, has been a strong advocate for allowing humanitarian access in Syria and sometimes clashed with Russia at the Security Council during his monthly reports on the worsening crisis.
During his last briefing to the council in late April, O'Brien said the humanitarian Syria's crisis was deteriorating and once again pleaded for action to stop the bloodshed.
The appointment of a new counter-terrorism chief, most likely from Russia, is the next personnel decision to watch along with the head of UN management, who will steer reforms.
The UN chief has continued his predecessors' practice of filling top posts with nationals from the five permanent Security Council countries -- Britain, France, China, Russia and the United States.
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