The Thai is ranked 54th in the world with the top 60 as of May 26 earning automatic places at the year’s second major.
The 44-year-old, who shared 38th place at last week’s European PGA Championship in England, will make his fourth appearance at the US Open, which will be held June 12-15.
After finishing 74th on his debut in 2001 and 47th in 2010, he missed last year’s cut by eight strokes.
Thongchai has qualified for all four majors this year. Ranked 24th in the Race to Dubai, Thongchai will take part in this week’s Nordea Masters on the European Tour.
Kiradech Aphibarnrat, meanwhile, has two more weeks to try to join Thongchai at the US Open.
His world ranking has dropped to 85th from 83rd after missing the cut at the European PGA Championship.
The 24-year-old must be in the top 60 by June 9 to secure a US Open berth. He will play in this week’s US$6.2 million Memorial on the PGA Tour.