Thai started as Thai Airways International, a joint venture with Scandinavian Airlines System (which initially held a 30% share), along with a domestic carrier, Thai Airways Company. The carrier's first flight was on May 1, 1960. On April 1, 1977, the Thai government bought out the remaining 15% of SAS-owned shares. On April 1, 1988, the two carriers merged to form the present Thai Airways International.

In August 2005, Thai Airways International president Kanok Abhiradee was suspended from his managerial duties just before the airline reported a massive loss for its fiscal third quarter to June 30. Following the suspension, the airline appointed board member Somchainuk Engtrakul to oversee Kanok's major responsibilities. The airline has named a new president in April 2006. As most tourists to the country come from Europe, Thai has a limited presence in North America, where its flights are marketed by Lufthansa. The arrival of the A340-500 coincided with a change to the airline's image, including a new livery and a revised font for the title "Thai". On May 1, 2005, the airline began a non-stop Bangkok-New York service (TG790/791) with a new A340-500. The New York bound flight time is 16 hours 55 minutes and Bangkok bound flight time is 17 hours 10 minutes. It flies over the North Pole, and departs at midnight (Bangkok time 0040 at summer).

Non-stop Bangkok-Los Angeles service (TG794/795) started on December 2, 2005, also using a new A340-500. The flight time is 16.5 hours eastbound. This replaces TG774/775 (LAX-KIX-BKK & BKK-KIX-LAX) service using Boeing 747-400 aircraft and the stop at Kansai International Airport in Osaka. In February 2006, the airline announced it was studying the startup of a new airline, to be called Thai Orchid , which would market itself as a luxury alternative to the low-cost carriers, such as subsidiary Nok Air. In June 2006 Thai International Airlines was awarded 'Worlds Best Cabin Staff' by Skytrax. Thai Airways International will be operating three weekly direct flights on the route Bangkok – Johannesburg v.v., utilizing A340-600 aircraft from October 2006.

Thai Airways Boeing 747-400 taking off On September 28, 2006 at 1:45am, flight TG 662 to Shanghai was the last Thai Airways departure from Don Mueang. At 4:45am, TG 613 from Delhi was Thai Airways' first official arrival at Suvarnabhumi.

Like all airlines, Economy Class is the cheapest class on Thai. Seat pitch on Thai Economy offers passengers up to 36" pitch in selected aircraft with an average of 34" on all aircraft. All Economy seats in Airbus A340-500, Airbus A340-600 and Boeing B777-200ER have individual Audio-Video On Demand (AVOD) In-flight Entertainment (IFE) system. Passengers will be given a choice of Thai or Western meals. Alcoholic beverages are free and served to passengers over the age of 18.

The new Premium Economy Class is only available on trans-continental flights between Bangkok(BKK) and Los Angeles(LAX) or New York(JFK) on Airbus A340-500 aircraft. The fare for Premium Economy Class is slightly higher than Economy but lower than Royal Silk (Business) Class. Premium Economy seating is configured as 2-3-2 rather than the standard 2-4-2 in Economy. Seat pitch is increased to 42", 135 degree angle of recline and the seat features a leg-rest. Premium Economy class passengers also have more choices over their meal selection. On some long-haul routes such as Bangkok - Copenhagen, aircraft with previous generation Business Class seats are used - therefore the seats are sold under Premium Economy Class fare.

With higher fares, Royal Silk Class passengers enjoy a number of priorities and luxury not available to Economy Class passengers. This includes dedicated premium check-in facility at Bangkok Suvarnabhumi International Airport, dedicated check-in desks at major airports around the world, lounge access, priority boarding, pre-flight champagne, fast track lane for passport control and security-check, and priority baggage handling. The new shell angled lie-flat business class seats are installed on 12 Boeing 747-400 aircraft, all Boeing 777-200ER aircraft, all Boeing 777-200 aircraft, all Airbus A340-500 aircraft and all Airbus A340-600 aircraft. The pitch is 60" between seats and width is 20".

When fully reclined (electrically adjusted) the seat become completely flat, however it is angled. The seat can perform lumbar massage. All seats are equipped with AVOD IFE. There are more choices of main course meal selection in Royal Silk class on international flights, although some may be identical to Economy Class offering. Premium alcoholic drinks are served with a more extensive choices of wine. Port and cheese is served after lunch and dinner.