Singh, who had assumed charge on January 1, 2012, had succeeded 'Metro Man' E Sreedharan.
He will continue to lead Delhi Metro Rail Corporation (DMRC), a joint venture of the Centre and the Delhi government, till December 2020.
The Delhi government had earlier proposed a five-year extension to Singh, who was to hang his boots on December 31.
"The govt of NCT of Delhi, in accordance with provisions of Article 130 of the Memorandum and Articles of Association of DMRC and after obtaining concurrence of the Central government, is pleased to extend the tenure of Mangu Singh up to 14.12.2020," read the order signed by the Transport Secretary of the Delhi government.