The aforementioned event honours the employees who were killed in the 9/11 terror attacks and witnesses celebrities making calls and raising money to benefit the charity of their choice.
The 32-year old who recently received treatment for alcohol addiction worked to gain donations for his charity of choice, Mencao - supports people with learning disabilities.
"My cousin Laurent is one of the 1.5 million people in the UK who has a learning disability," Harington said.
"People who have a learning disability need extra support to lead the life they wish to. Mencap has supported my cousin to live the life he wants and that's why I am proud to support Mencap," he said while voicing his support for the charity of his choice.
Amongst the other attendees was the Duke of Sussex, Prince Harry who was also clicked holding two phones simultaneously.
On the work front, Harrington was last seen in the finale season of the much-loved HBO show 'Game of Thrones' where he starred as Jon Snow.
The series' last episode aired on May 19 this year.