Chapchai is the son of a Thai national team golfer, and turned professional in 1998 as a fifteen-year-old.

He won for the first time as a pro at the 2004 Genting Masters in Malaysia.

He joined the Asian Tour in 2005, and had a second-place finish in his rookie season.

In March 2009, Nirat shot 32-under-par over 72 holes to claim the SAIL Open, setting a new Asian Tour record for the best 72-hole score.

"T" = Tied Note that the HSBC Champions did not become a WGC event until 2009.