Haiti enjoyed long periods of possession in the first half but wasted a good chance when Sony Alcenat's right cross was headed wide by Preux Leonel in front of the goal.
The second half was more of the same until midfielder Chris Birchall marked his return to Trinidad by sweeping a 61st minute free kick to an unmarked Thomas, who headed the ball past Haiti goalkeeper Fenelon Gabart into the right corner.
Free kick
In the 68th, Birchall floated another free kick to the back post where Thomas headed it across goal for Glen to chest the ball over the line.
It was the Soca Warriors' third successive 2-0 win after friendly victories over Guyana and Netherlands Antilles.
Both sides are preparing for the semi-final round of World Cup qualification. Trinidad face Cuba, Guatemala and the United States in their group while Haiti take on Suriname, El Salvador and Costa Rica.
The sides will meet in another friendly, in the Haitian capital Port-au-Prince, on August 10, before Trinidad visit Cuba, and Haiti host Suriname in their opening World Cup fixtures on August 20.