[5] He was also an active member of the College rifle shooting team, which won many coveted trophies and then later, he joined the army.

When Wanasinghe took command the army was engaged in subduing 2nd JVP insurrection in the south of the island, while the Indian Peace Keeping Force (IPKF) was present in North and East of Sri Lanka.

During his tenure he expanded the army and raised a number of new units including special forces and established its sniper school.

Indian Defence Review in 1991 reported that "Army Commander Lt Gen Hamilton Wanasinghe visited the battlefield frequently and narrowly escaped being killed."

Operation Balavegaya was launched in June 1991 with assistance of Sri Lanka Navy with an amphibious landing at Vetterlerkani which LTTE leader called it "Mother of All Battles".

He had a rare distinction of holding all three key appointments of the Sri Lanka's Defence establishment at a time country faced southern JVP insurrection and LTTE Second Ealam War.

[3][10] In November 1993 General Hamilton Wanasinghe facilitated the relief operation during the Battle of Pooneryn with an amphibious landing of Army troops assisted by the Navy.