Karachi Grammar School is also known for its Model United Nations team. It has entered competitions including LUMUN (Pakistan's largest international Model United Nations conference, hosting over 1200 delegates), where the school team won in 2008, 2009, 2012, 2015 and most recently, in 2019. Karachi Grammar School also took part in Harvard Model United Nations 2012 in Beijing, China, winning the 'Best Large Delegation' award. In August of the same year Karachi Grammar School sent a 12-member delegation to Hyderabad, India to attend the 2nd session of the Harvard Model United Nations India. Once more the delegation received the overall Best Large Delegation Award out of over 100 delegations and 800 delegates. This made the school the winner at both of Harvard's international high-school MUN conferences (China and India). In the following years, KGS was once again declared the Best Large Delegation at Harvard MUN India 2013 and Harvard MUN China 2014, 2015. Recently they won Best International Delegation at HMUN Boston 2016, as well as HMUN China in 2017 sustaining an undefeated streak at international MUN