Mandeep Singh came to notice with back to back centuries in his debut season for the Punjab Under-15 team in the 2005 Polly Umrigar Trophy, and further vindicated his growing talent in the next season where his scores of 113, 98 and 165 in the knockout games were instrumental in Punjab retaining the title. By 2009 his sparkling performances in Australia and South Africa for India Under-19 had earmarked him for the future. The seamless transition from junior cricket to first class cricket was reflected in his Ranji Trophy averages of 53.55 in 2010-2011 and 71.62 in 2011-2012. His stature grew further with a super season for Kings XI Punjab in IPL 2012, where he was the team's top scorer and spoken of as a 'certainty for the India cap' by David Hussey. Along with his batting, Mandeep also bowls useful part-time medium pace.