The municipality was founded in 1759 by the Marquis of Pombal, as a reward by King Joseph I to his minister for his efforts in rebuilding the Lisbon historical downtown (Portuguese: Baixa) after the 1755 Lisbon earthquake. His former residence, the beautiful Palace of Marquês de Pombal, is a typical 18th-century manor house that is worth admiring.
The growth of leisure activities along the coast transformed Oeiras, which became a privileged location for the Portuguese elite. The construction of the National roadway to link Lisbon to Cascais allowed new travelers to experience the zone, resulting in an influx of new residents that expanded the urban centers, giving rise to beach "chalets", summer cottages and luxury condominiums, near the Parque dos Poetas, a 10 hectares park dedicated to Portuguese poets.
At the end of the 20th century the municipality became known for its high standard of living and for its new technologies and service industries, with several multinational and technology companies, research institutions and business parks, becoming a sort of Europe’s “Silicon Valley”.
The elevated standard of living and work allowed the Town to obtain several awards, including the "Best Municipality to Work", "Municipal Excellency Award", "European Enterprise Award" and the "ECOXXI" Award.