Mahmood was commissioned in 2nd Battalion of The Baloch Regiment in 1960, when passed out from PMA in 1963. The same year, he was inducted in 51st Paratrooper Division, Airborne Corps, and from there, he was selected for the Special Services Group (SSG). After completing the Special Training of SSG he was posted to the 1st Commando Battalion(Yaldram)(Shaheen Company).
1965 Indo-Pakistani War
In 1965, SSG was preparing for covert Operations in Kashmir, meanwhile Captain TM was selected for an advance course with U.S. Army Special Forces, but he opted himself for covert operations instead of leaving for United States to attend the advance course. He was awarded Sitara-e-Juraat (SJ) for his acts of bravery during Indo-Pak war of 1965. Tariq Mahmood was promoted to the rank of Major in 1970 and was stationed in Peshawar. Major TM was posted as the commandant Parachute Training School.
1971 Winter War
In 1971, Major TM volunteered to go East Pakistan to participate in Indo-Pakistani War of 1971. He was an officer in command and had received direct orders from General Amir Abdullah Khan Niazi. General A. A. K. Niazi had given him a direct order, and told him ""if you hear or see the fire, burn the place down". In a conflict, Major TM was sent to Shahjalal International Airport (Dhaka Airport) to lead an operation against insurgents. The Airport was heavily guarded by the insurgents and it was considered no-fly zone. Major TM commanded the Shaheen Company, 1st commando battalion and his company saw the heavy fighting in the Airport. After 34 hours of tiring battle, the Shaheen Company, 1st commando battalion gained an absolute control of the Airport and its surrounding areas, and it was freed from the insurgents. Both sides have had suffered heavy casualties and the Airport was nearly destroyed in the battle.
While in East-Pakistan, Tariq Mahmood was assigned another mission. He was sent to Northern Bangladesh, where he sat to led a covert operations against the insurgents. He was a commanding officer of the 25 SSG officers of Shaheen Company,1st commando battalion, saw the bloodiest and gruesome battle near at the river. The Shaheen Company, 1st battalion, re-captured and gained control of a bridge over the Brahmaputra River from the enemy. While commanding the operation, Major TM was hit by two bullets in his leg but continued to fight and lead the operation till the mission was successfully complete. After the operation, the Shaheen Company, 1st battalion was re-called to Dhaka. Major Tariq Mahmood was the last Pakistani soldier to leave East-Pakistan, commanding the C-130 aircraft departing from Dhaka Airport in 1971.
After the war, in 1971, Major TM was awarded his second Sitara-e-Jurat, and was stationed in Lahore. In 1973, he posted to 3rd Commando Powinda Battalion, and was promoted to the rank of Lieutenant-Colonel in 1974. In 1977, he was made Commanding officer of the 3rd Commando Powinda Battalion, SSG Division. In 1977, he saw his battalion in action against the heavily armed Pashtun tribes in Northern Pakistan who blocked the Karakoram Highway which links Pakistan and China. In the summer of 1977, the Government of Pakistan had asked him to lead an operation against the belligerents. Lt. Col. TM was given the task to get the road opened and cleared the designated area from the insurgents. Lt. Col. TM delivered a quick and immediate military operation against the tribes and completed the mission with full success. In his recognition, the Government of Pakistan awarded him Sitara-e-Bisalat in 1977.
1984 Siachen War
In 1979, he was promoted to Colonel, and in 1982, he was promoted to the rank of Brigadier. Brigadier TM, now a one-star general, was made commandant of the Special Services Group. In 1984, Brigadier TM commanded the Special Services Group at Siachen Conflict. SSG launched an aggressive and quick operation against Indian Army. Brigadier TM led a mild victory in 1984, and the control of the Siachen glacier was given to X Corps headed by Colonel-Commandant (X Corps) Lieutenant-General Zahid Ali Akbar. However, the territory was lost when Indian Army launched a successful military operation, Operation Meghdoot, which resulted in an absolute control of Siachen glacier by Indian Army. Brigadier TM, in retaliation, launched covert operations which continued until his death. The Pakistani ISI learnt that India's secret agency RAW had received order to attempt an assassination on Brigadier TM, and Indian Prime minister Rajiv Gandhi was reportedly briefed once a week about the activities of TM. After this report, the security of Brigadier TM was further tightened by Pakistan Army.
Throughout the 1980s, the SSG and ISI were closely collaborating with the U.S. Special Forces and Special Activities Division in order to lead the secret operation known as Operation Cyclone. Brigadier TM was also a commanding officer of the Battle for Hill 3234, and the operation was fully executed by the Brigadier TM. On 5 September 1986, Pan Am Flight 73 was hijacked in Karachi, Sindh. Brigadier-General Tariq Mahmood quickly came to Karachi where he led the planning of the operation to free the Airline from terrorists. He came to public prominence when he had led the successful Operation PANAM to liberate the Airline from terrorists. The hijackers opened fire on SSG team, killing and injuring the passengers but due to SSG’s quick action soon all the hijackers were arrested saving many lives. In the later 1987–88, he led operations against criminals in Sindh.