Compliance with the Paris Agreement requires the transformation of national economies to meet net-zero carbon dioxide emissions by mid-century. To accomplish this, countries need to define long-term decarbonisation strategies with near- and mid-term actions to determine their ideal future scenario while maximizing socioeconomic benefits. This paper describes the process followed to support the creation of the decarbonisation pathway for the transport and energy sectors presented in Costa Rica's National Decarbonisation Plan. We discuss in detail the technological pathway of a deep-decarbonisation future that supports reaching net-zero emissions by 2050. Compared to a business-as-usual (BAU) scenario, our results show that the decarbonisation pathway can lead to emissions' reduction of 87% in the transport and energy sectors by 2050. Energy efficiency, the adoption of electromobility, modal-shift towards public transport and active mobility, as well as reduced demand due to digitalisation and teleworking, are found to be key drivers towards the deep-decarbonisation. These measures combined enable a 25% reduction of primary energy production by 2050. The results highlight that the decarbonisation scenario requires installing 4.4 GW more of renewable power plants by 2050, compared to the BAU scenario (80%). We also show that additional investments for the deep-decarbonisation are compensated with the reduced operating cost. Crucially, we found that the National Decarbonisation Plan results in a lower total discounted cost of about 35% of current Costa Rica's GDP, indicating that a deep decarbonisation is technically feasible and is coupled to socioeconomic benefits.