A career diplomat, Khan is expected to assume his new post later this month.
Haroon, 61, had been Pakistan's envoy to the UN since September 2008 and lead his country to win a seat as non-permanent member of the Security Council for two years in elections held last year.
He shares cordial relations with India's Permanent Representative Hardeep Singh Puri and had participated at the celebrations organised by the Indian mission here to commemorate Mahatma Gandhi's birthday at the UN headquarters on October 2.
The International Association of Permanent Representations to the United Nations (IAPR) had hosted a farewell reception yesterday for Haroon where his counterpart from Kazakhstan lauded the work done by Haroon in his four years at the UN.
Kazakh Ambassador Byrganym Aitimova said Haroon was a popular figure at the UN who would be missed by his colleagues.