THAI began to evaluate the size of its fleet, and specifically what would it replace the CV-990 with. The obvious choices were the Boeing 707 or DC-8, but both were too large to operate on THAI’s short-medium haul routes. However, it selected the Caravelle with its high standard of comfort, and reduced the normal five-abreast 89 seats to a four-abreast 72 seat layout. The first of five examples entered service on January 1, 1964. When its fifth Caravelle was delivered in 1966, the last DC-4 was retired; allowing THAI to enjoy the distinction of being the first all-jet airline in Asia.

Encouraged by the success of its Bali services, THAI launched flights to the Nepalese capital, Kathmandu. In early February 1969 the airline began upgrading its fleet, initially leasing two DC-9-41s from SAS. Supplementing the DC-9s, it also leased two 146-seat DC-8-32s for use on its long-haul flights. The original ten-year contract with SAS expired in 1970 and both parties were keen to sign an extension to the co-operation agreement, this one lasting for seven years.

On April 1, 1971 it launched a new service to Sydney via Singapore and/or Bali. Two years later, on June 3, 1972 THAI launched its Royal Orchid Service to Europe, flying from Bangkok to Copenhagen with a technical stop in Moscow. The route was made with the stretched DC-8, the -62 series, again leased from SAS. On November 2, 1973 a second Trans-Asian Express route was added, from Bangkok to London via Tashkent. This allowed the airline to fly a through service from London to Sydney, which took just over 20 hours to complete, with two stops in Bangkok and Singapore.

In the mid 1970s, THAI began to reduce its reliance on SAS. It started acquiring additional DC-8s by lease-purchase agreements through the First National City Bank. The Thai Government extended SAS’s contract again on July 16, 1974 but agreed to halve its shareholding from 30% to 15%. THAI flew is first DC-10 service to Amsterdam in March 1975, resplendent in a new stylish livery developed by Walter Landor Associates. The old Thai dancing figure was replaced by a distinctive purple, pink and gold symbol.

On 1 April 1977, after 17 years of capital participation by SAS, the Thai government bought out the remaining 15 per cent of SAS-owned shares and THAI became an airline owned by the Thai government. Also during 1977 the first Boeing 737-200 arrived and the last version of the DC-8, the -6. One year later, THAI operated its first services to North America in 1980.

With a surge in air travel around the world and to Thailand in particular, the company took the decision to upgrade its fleet with more wide-bodied airliners. The carrier’s first-owned DC-10-30 (the previous example had been leased) arrived in 1978 and was joined by the Airbus A300B4 later that year. On November 2, 1979, its initial B747 arrived and immediately launched non-stop services from Bangkok to Europe.

It had to wait until March 30, 1980, before it finally launched its own trans-Pacific flights, between Bangkok and Los Angeles, with intermediate stops in Tokyo and Seattle. The company’s Royal Executive Class was initially introduced on its regional flights, offering passengers upgraded standards in comfort and convenience. The HS 748s were eventually replaced by Shorts 330s and Shorts 360s for domestic flights, from 1982.

A new Maintenance Centre was opened at Bangkok International Airport in 1985 to cope with the maintenance of the ever increasing of aircraft types. Also in 1988 the first Airbus A310 arrived.

Although, the domestic division of THAI was known as just Thai Airways, towards the end of the 1980s the time was right to rationalise the peculiar situation that both carriers found themselves in, with the small domestic company being a shareholder of the national airline. In the best interests of both organisations they agreed to merge on the 1 April 1988. The new combined carrier operated 41 airliners across a network of 48 destinations in 35 countries as well as 23 cities in Thailand, at the time.

As the unified national airline entered the 1990s, it faced tremendous passenger growth. It required larger aircraft on all fronts, so it leased a fleet of eleven British Aerospace BAe 146s for its domestic operations, while more bigger Airbuses A300-600Rs, were acquired for its regional routes around Asia. Additional B747s, including the -400 series, were purchased to enable it to keep pace with its competitors, the first to arrive in 1990. Its older DC-10s were replaced during 1991/92 by McDonnell Douglas MD-11s.

In 1992 the THAI Government announced its intention to privatise THAI, beginning with 100 million company shares being listed on the Bangkok Stock Exchange. Two years later, on May 20, 1994 THAI was officially registered as THAI Airways International Public Company Limited. The airline continued to invest in new state-of-the-art aircraft, its first Rolls-Royce Trent 800 powered B777-200 was delivered during 1996.

On 14 May 1997, THAI, along with Lufthansa, Air Canada, SAS, and United Airlines, founded the world's first and largest airline alliance, Star Alliance. It also received its first of eleven A330s that joined in the late 1990s.

Throughout the 2000s, THAI aggressively continued its route network expansion with new services to Chengdu, Busan, Chennai, Xiamen, Milan, Moscow, Islamabad, Hyderabad, Johannesburg (later suspended) and Oslo. THAI took another major step in its long-term fleet expansion plans in August 2004 when it announced it was placing firm orders for six A380.

Also, after almost a quarter of a century since its existing branding had been introduced, THAI decided to unveil a spectacular new corporate image on April 7, 2005.

As well as the obvious changes to its aircraft livery, the rebranding influenced a wide range of products from cabin interiors to ticket offices. The first of the company’s fleet to wear the revised livery was a B747-400. As part of the launch celebrations, THAI took delivery of its initial A340-500 (HS-TLA), also with the new livery on the 06 April 2005. The arrival of A340-500, with it extraordinary long range, enabled THAI to launch non-stop Bangkok to New York services, a 17 hour, (14,020km) journey.

The delivery marked the start of a major Airbus wide-bodied fleet expansion under which six A340-600s and three more -500s were delivered by 2008. Using the Airbus A340-500s, the airline later converted existing one-stop services to Los Angeles into non-stop services using the same aircraft type.

In 2006, THAI moved its hub operations to the new Bangkok Suvarnabhumi Airport.

Also after 2006, Thai made Phuket airport into its secondary hub by launching direct destinations such as Hong Kong or Tokyo. However, THAI's aggressive growth was hampered by a combination of internal and external factors, including a spike in fuel prices, domestic political conflict in Thailand, and the global economic crisis of the late-2000s. In 2008, after achieving profitability for the previous 40 years, THAI recorded a loss for the first time in its history. As of 2009, after a series of restructuring initiatives, including a two-year deferral of its Airbus A380 deliveries, the carrier returned to a net profit.

Citing very high fuel costs, THAI discontinued the New York service in July 2008, even though the airline had been able to fill 80 per cent of the seats. The service to Los Angeles was again reverted to one-stop service via Seoul on 1 May 2012, leaving the airline without a non-stop service between Thailand and North America. The A340s were then replaced by used Boeing 777-200ER for the Bangkok–Seoul– Los-Angeles route, and later with Boeing 777-300ER, delivered from May 2010.

While celebrating its 50-year anniversary in 2010, THAI, began plans for the airline's future, including aircraft fleet renewal and an upgrade of existing services. THAI placed orders for a number of aircraft, including the Boeing 787 and Airbus A350, and also launched a refurbishment of its Boeing 747 and 777 cabins. THAI also resumed its network expansion with the resumption of flights to Brussels, in addition to a new non-stop flight from Stockholm and Copenhagen to Phuket. At the same time, the Greek debt crisis caused THAI to suspend its services to Athens.

As part of THAI's broader growth strategy in the region, THAI launched a regional carrier with light-premium services in July 2011, Thai Smile, which operated the narrow-bodied Airbus A320-200 on regional and domestic routes. (Read more about Thai Smile).

In 2012, Thai Airways officially entered the "superjumbo" era when it took delivery of its first Airbus A380-800 (registration HS-TUA, named "Sri Rattana") on 27 September 2012 at the Airbus headquarters in Toulouse, France. The airline marked the occasion with a grand inaugural service from Bangkok to Hong Kong on 6 October 2012.

During the initial launch phase, the A380 was deployed on regional "shuttle" routes to Hong Kong and Singapore before transitioning to flagship long-haul services to Frankfurt on 15 December 2012, followed by Tokyo (Narita) and Paris in early 2013 and then on to London Heathrow (LHR) on 1 July 2015 operating flight TG910/TG911. 

The aircraft featured a spacious three-class configuration designed to carry 507 passengers in total, with 12 Royal First Class suites on the upper deck, 60 Royal Silk (Business) Class staggered lie-flat seats, also located on the upper deck and then

435 Economy Class seats, split between a small cabin on the rear of the upper deck and the entire main deck.  

During July 2014, the first 787-8 aircraft operated its first commercial flight from Bangkok to Chiang Mai. With the delivery of the second 787-8 aircraft, THAI operated it to and from Perth, Australia and Bangkok to Haneda, Japan.

On 1 December 2015, the US Federal Aviation Administration (FAA) announced their reassessment of the safety rating for Thailand, downgrading it from a Category 1 to Category 2 country, the rating means that the country either lacks laws or regulations necessary to oversee air carriers in accordance with minimum international standards. With a Category 2 rating, Thailand's air carriers could continue existing routes to the United States but they won't be allowed to establish new routes to the United States. The European Aviation Safety Agency (EASA) declined to blacklist any Thai carriers following a review of certain carriers in November 2015. THAI later received third country operator (TCO) certification from the EU, effective 15 December 2015, authorizing the carrier to continue flying to the EU for the foreseeable future.

In order to improve its rating and services, the airline was forced to implement some changes. As a consequence, in July 2015, THAI announced the planned cancellation of services to Los Angeles after October 2015, marking the end of US services all together. It also received 14 new Boeing 777-300ERs, delivered between 2014 and 2015. In June 2016, as a result of its reconstruction plan, THAI announced to commence thrice-weekly Tehran service (however, later it stopped its service on 28 February 2018) and resumed Moscow services from October 2016. New Airbus A350-900 arrived from August 2016, and operated flights to Europe.

The airline also considered a return to the US using Boeing 787-9 by 2017. However, the THAI president, turned down the possibility of returning to Los Angeles or New York City due to losses in the past. Instead, THAI eyed other cities such as San Francisco and Seattle. However the USA routes were not materialised.

Later, in August 2016, THAI introduced new route network management system. In which many of its regional flights would be flown by its subsidiary, Thai Smile. As well it would allow for more connectivity at its major hub at Bangkok by linking transit flights with it’s major international network.