Singh's addition Wednesday was a key boost for Woods, who last week said he was having a difficult time getting top golfers to commit for the July 5-8 tournament at Congressional Country Club. The tournament was added to the PGA Tour calendar in March, after most players had set their schedules for the year.
Singh, ranked No. 6 in the world, has won three majors and has two victories this year on the tour.
Woods himself is uncertain if he will play because the tournament could coincide with the birth of his first child.
The AT&T National will be an invitation-only tournament with a 120-man field.