Mithun started his golf carrier as a junior golfer at the age of 11, being runner-up in the Sri Lanka Junior under 15 championships 1997. He won the Junior under 15 Championships in 2000 followed by winning the under 18 Championships in 2002, 2003 and 2004.
The Committee also extended him the facility to become a RCGC member in 2004, as was done with Nande. He quickly won the RCGC Championships on four occasions and also won the foursomes RCGC Board event of the Shakspeare Shield. He continued to have a string of victories from 2005 to 2010 both in Sri Lanka and abroad winning the Sri Lanka Amateur Championship in 2006 and 2008, SAARC Golf Championships both Individual and Team events in 2007, the East India Amateur Championship in 2007, the Mission Hills Asia Pacific Amateur Championship 2009 and the Surya Nepal Amateur Championship 2009. He has had Runner‑up finishes in the Hong Kong Amateur 2005, Pakistan Amateur 2006 and 2008, Malaysia Amateur 2009.
In 2010 he added a further string of wins as Championship Winner of the All India Amateur Championships, Bangladesh Amateur Championships, Saujana Amateur Championships, Singapore Amateur Championships and Sri Lanka Amateur Championship all in the same year.
He turned as a Pro in 2011 at age of 25 years. He played in the Asian Circuit, Indian Circuit and European Tour events and was Winner of the Louis Philippe Cup 2012, Tata Open 2012, Standard Chartered Open 2012, PGTI Eagleburg Open 2014, Louis Phillip Cup 2014 and Standard Chartered Open 2014, which were all Indian Circuit and Asian Circuit Tour events. In the same period when he did not win, he had high finishes in the Pro circuit tournaments he played. His finishes in the ISPS Honda Singapore Classic Asian Tour 2nd, Myanmar Open Asian Tour 2nd, Hero Indian Open 9th, Resort World Manila Masters 9th, Mcleod Russel Tour Championships 8th, European Tour Gujarat Kensville event 28th and Avantha Masters European Tour event 29th , amongst the many other events he played.
Mithun is rated today, as Sri Lanka’s best golfer from the many other emerging RCGC golfers and caddie golfers who have played with him in the Amateur and Pro Tournaments. His prize money in the Pro circuit makes him stand out alone as the best golfer Sri Lanka has produced.
He holds the Amateur Course records of RCGC at 9-under, Victoria Golf Course at 7-under both established in 2010 and the Bombay Presidency Golf Club of 8-under established in 2014. He still plays in the pro circuit and continues his golf practice routines at RCGC, under the watchful eye of father Nande.