was for many years the longest runway in Africa. U.S. President Franklin D. Roosevelt had lunch with President Edwin J. Barclay at Roberts Field during his visit to Liberia in January 1943. From 1943 to the end of World War II in 1945, Roberts Field Airport, as it was then known, served as an alternative base for a contingent of 26 Squadron SAAF which flew Vickers Wellington bombers on anti-submarine (U-Boat) and convoy escort patrols over the Atlantic. Their main base was at Takoradi, in the Gold Coast.

Pre-war commercial area:An aerial view of the airport in 1997

The story of Robertsfield is consistently intertwined with the history of Pan American World Airways. In fact, from the end of World War II until 1985, the airport was administered and operated by Pan American under contract with the Republic of Liberia's Ministry of Transport. Monrovia was consistently a key link in Pan American's African network, usually an intermediate stop between Accra and Dakar, from which service continued onward to Europe and New York.

In the late 1970s and into the early 1980s, the airport became Pan Am's principal African hub, with a nonstop Boeing 747 service from New York JFK connecting at Robertsfield to such destinations as Dakar, Accra, Abidjan, Lagos, and Conakry, among others, and continuing on to Nairobi and even at times Johannesburg, so that for many years virtually every Pan Am passenger to Africa passed through Robertsfield. Pan Am's presence diminished during the 1980s, as Pan Am's African network was slowly pulled down. Pan Am ended its management of the airport in 1985[8] but as late as 1986 the airport was still a stop on the JFK-Dakar-Monrovia-Lagos-Nairobi route. By 1987, Pan Am was no longer serving Monrovia at all.

A number of European airlines also served the airport from the mid-1960s to the mid-1980s, including British Caledonian Airways with Boeing 707s, KLM Royal Dutch Airlines with Douglas DC-8s and Sabena, Swissair and UTA with these three air carriers all operating McDonnell Douglas DC-10s into Robertsfield. Scandinavian Airline System also served Monrovia, from Copenhagen. In the mid-1970s this service consisted of a weekly flight via Düsseldorf and Madrid and a second weekly flight via Zürich, then onward to South America: Rio de Janeiro, Montevideo, and Santiago de Chile.

Similarly, VARIG employed RIA as a stop on its flights between Brazil and Europe, which began in the mid-1960s and lasted at least until the mid-1970s, with various routings including Rio de Janeiro-Monrovia-Rome and Rio-Monrovia-Madrid-Rome. VARIG's Flight between Rome and Rio crashed at Monrovia in March 1967, and remains the worst aviation accident in Liberia to this day.

As with Pan Am, several African flag carriers utilized Robertsfield as a waystation on transatlantic routes. As early as 1966, Nigeria Airways began a codeshare cooperation on Pan Am's flights to New York-JFK from Lagos via Monrovia, and in later decades Monrovia remained a stop on its weekly services to New York, at most times utilizing its own McDonnell Douglas DC-10. This also included for a time a weekly Monrovia-Port of Spain-Miami flight. Until 1983, Air Afrique's DC-10s also stopped at Robertsfield on that airline's Abidjan-Monrovia-Dakar-New York services. Likewise, Zambia Airways made two stops per week at RIA on the way to New York-JFK from Lusaka, a service which commenced in April 1988[17] with a DC-10 and lasted until 1992.

In the past, Roberts Airport was listed as an alternative landing site for NASA's Space Shuttle.

Post-war redevelopment: The passenger terminal at Roberts International Airport in 2006.

During the Second Liberian Civil War, the main terminal building suffered major damage, and remains vacant and unenclosed. Currently, the terminal facilities consist of two passenger buildings, one for departures by most commercial carriers and all arrivals, and a second, Terminal B, opened in March 2012, and in its first two years was reserved exclusively for departures by Air France and Delta Air Lines. Other airside buildings are primarily used by the United Nations, with a VIP facility adjacent to the original, unused terminal.

After the end of the civil war in 2003, commercial air service was slow to return to Liberia, and only gathered momentum after the inauguration of President Ellen Johnson Sirleaf in January 2006. Royal Air Maroc started flights to Mohamed V International Airport in November 2007, and Virgin Nigeria added Monrovia to its network, from Lagos via Accra twice per week, in October 2008.

Also in October 2008 U.S. carrier Delta Air Lines announced that, as part of a major expansion of its route network in Africa, it would begin a once-weekly service between Atlanta and Monrovia, via Sal, Cape Verde. The proposed service would have commenced in June 2009, utilizing a Boeing 757-200 configured for ETOPS operations in a two-class configuration. The news marked the return of an American carrier and direct flights to the United States for the first time since Pan Am's withdrawal, and would make RIA one of only a handful of African airports with service to the US, so was therefore seen as a major step in the recovery of not just the airport, but Liberia itself. The route was revised in May to originate from New York's JFK and connect via Dakar, beginning on 9 June, Monday, and returning every Tuesday.

One week prior to the inaugural flight, Delta announced that its planned launch would be suspended indefinitely. It was reported widely that the carrier had been denied permission by the Transportation Security Administration due to a lack of acceptable security standards at Robertsfield. Neither Delta nor the TSA issued any further explanation. However, Cynthia B. Nash, a prominent Atlanta businesswoman, stated in an interview coinciding with her appointment as Liberia's Honorary Consul in August 2009 that she expected Roberts International to upgrade its security to meet TSA standards and for the Delta to launch the flight "within the year." Coinciding with these comments, it was reported in the Liberian press that a division of Lockheed Martin was to take over management of Robertsfield.

Delta Air Lines inaugural flight to Monrovia (5 September 2010)

On 5 September 2010, Delta launched once weekly flights between Atlanta and Monrovia; with a stop in Accra. In January 2011, Delta Air Lines increased flights to twice a week (Sundays and Wednesdays). By mid-2012, Delta operated a Boeing 767-300 thrice-weekly to and from New York-JFK, while maintaining the stop in Accra.

In April 2011, Air France launched a twice-weekly Airbus A330 service to and from Paris CDG, initially as an extension of its services to Conakry and later paired with a stop in Freetown. British Airways was the next airline to launch new service to Monrovia, commencing twice-weekly flights from London Heathrow to RIA as an extension of the London-Freetown flights that BA had taken over from its merger with BMI. The service began in November 2012 with a B767-300ER.

As a result of these developments, throughout 2013 Roberts International Airport offered passengers same-plane service to Atlanta, Brussels, London and Paris more than once per week.

Daily commercial traffic peaked in this year, with one or two daily arrivals. The busiest and most frequent connection was to Accra, with four airlines providing at least one flight per day on the route, which for a time made it the third-busiest connection from Accra and one of the top 15 route pairs in West and Central Africa,[31] although service on the route has diminished in 2012 with the end of Air Mali's unsuccessful Bamako-Monrovia-Accra service[32] and the demise of Air Nigeria,[33] which for several years had flown from Lagos to Monrovia via Accra five times per week.

In October 2012, start-up airline Gambia Bird commenced twice-weekly non-stop services between Banjul and Robertsfield with an Airbus A319. This service was later expanded to include multi-week flights to Accra and Freetown, and by mid-2014 Gambia Bird had offered the most destinations from Robertsfield of any airline, with same-plane service to Lagos, Douala and Dakar. Also in early 2014, Air Côte d'Ivoire added a service from Abidjan to Freetown via Roberts International.

Decline of service and effects of Ebola crisis: A decline in global prices for commodities such as gold, iron ore and oil began in 2013 and 2014, causing an immediate slowdown of Liberia's extractive-dependent economy, which in turn pressured the viability of the many new intercontinental services from Robertsfield. The first major blow to the airport's renaissance came in late June 2014, when Air France scrapped its flight to Liberia, citing lack of profitability.

An even bigger loss to the airport in terms of capacity, connectivity and prestige came when Delta Air Lines announced that, after nearly four years of service, it would cease flights to Monrovia on 31 August 2014 due to weak passenger demand.

Within the same month that the last Delta jet departed Liberia, most scheduled flights, including those of British Airways, Kenya Airways, Air Côte d'Ivoire, Arik Air, and Gambia Bird were suspended due to the rapidly-spreading Ebola outbreak. Royal Air Maroc and Brussels Airlines both remained flying through the crisis, albeit with reduced schedules. British Airways and Delta have not resumed service to Monrovia since that time.

Gambia Bird subsequently ceased operations entirely, in large part because of the downturn in air travel across West Africa due to Ebola. The first airline to return service to Robertsfield was Air Côte d'Ivoire, in October 2014. Kenya Airways returned thereafter, resuming its Nairobi-Accra-Monrovia flights in January 2015 after the Kenyan Ministry of Health lifted its restrictions. In September 2015, Brussels Airlines brought back more frequencies to its Monrovia service, doubling weekly flights from its twice-weekly low during the Ebola crisis back to four per week, similar to its pre-Ebola capacity.

Although Air France did not resume its connection to Paris, its subsidiary KLM announced in October 2016 that it would return to Monrovia for the first time in decades, with a thrice-weekly Amsterdam—Freetown—Monrovia service using an Airbus A330. KLM's flights began in March 2017, but lasted less than two years, as in October 2018 KLM announced the closure of the service in January 2019. This reduction once again left Brussels Airlines as the only intercontinental connection out of Liberia, until Air France announced in November 2019 that it intended to extend its daily Paris—Bamako flights onto Monrovia, which, after a delay due to the COVID-19 pandemic, finally began in November 2020 utilizing an Airbus A350 and stopping in Bamako in both directions. Air France terminated its connection to Monrovia in April 2022.