Kayani was hand-picked by former military ruler Gen Pervez Musharraf as the army chief in 2007. He was given an unprecedented three-year extension by then premier Yousuf Raza Gilani in 2010.
The selection of the chief of the Pakistani army, often described as the state within the state, has not been an easy task for the civilian government and especially for the once bitten, twice shy Sharif.
This would be the fourth time he would be choosing an Army Chief.
He picked up Abdul Waheed Kakar as the Army chief in 1993 but the General soon ditched him and played a key role in Sharif's resignation. Kakar had superseded at least four senior generals.
In 1998, he hand-picked Pervez Musharraf to head the Army and he too had superseded at least two Generals.
Musharraf first plotted the Kargil misadventure derailing Sharif's India-Pakistan peace dialogue in 1999 and then engineered a coup against the Prime Minister in the same year.
Sharif selected Ziauddin Butt in October 1999 but he could not take over as the Army chief due to the coup by Musharraf.
Kayani, who also served as the Director-General of the spy agency Inter Services Intelligence (ISI) and director of the Directorate-General of Military Operations, will hang his boots on Friday after being at the helm of the Army for six years.
The position of the Chairman Joint Chiefs of Staff Committee has been vacant since the retirement of Gen Khalid Shamim Wynne.
This position, though traditionally held by the Army, is actually meant to be shared on a turn-by-turn basis between the three services - the Army, the Navy and the Air Force.
