[1] The toponymy Seixal comes from a type of smooth stone (seixo) that is found in rivers; the name evolving from the name used to describe the geomorphology of the region.

[2] In the 15th century, due to its prime location, various dockyards and shipbuilders began constructing river boats and trans-Atlantic ships.

After the Liberal revolution, during the administrative reforms of 1836, during the reign of Queen Maria II of Portugal, Seixal obtained the status of municipality.

The Bay of Seixal is part of the Tagus River Estuary, that is fed by several rivers and confluents that extend to the sea; classified as a Reserva Ecológica Nacional (National Ecological Reserve), the bay and small tributaries are part of one of the most important humid zones in Portugal, supporting an elevated biodiversity and exceptional landscape.

[3] Seixal is one of the eight municipalities with the most inhabitants in Portugal, and is composed of four parishes occupying a territory of 95 square kilometres (37 sq mi):[4] Although the municipal population continued to grow with development, after the 1970s there was a boom in the population, due to improvements in accessibility and mobility, principally due to public transport, its location to Lisbon and installation of economic activities within the territory.

[3] This growth transformed, in a short time, from a territory predominantly rural into an urban municipality, consisting of agglomerations of large dimensions focusing on various establishments and social centres.

[3] Two of the most recent investment catchment operations is Seixal Business Park, an area next to the Coina node where are headquartered 69 companies, representing about 1,500 jobs, and the study redefine the spatial organization of the area occupied by the former National Steel Company (Siderurgia National do Seixal).

With a wide river front and a large area of tree mass, there are numerous business activities with potential for tourism and leisure.

The principal road network that crosses the municipality, guarantees the connections north to Almada and Lisbon, some 15 kilometres (9.3 mi) away, in addition to Setúbal, including the A2 motorway.

[3] The A33 motorway also constitutes a vital variant along the Setúbal peninsula, allowing connection along two bridges over the Tagus, and facilitate inter-municipal commerce.

Throughout there are secular or religious celebrations that highlight the calendar year, including the Modern Music Festival of Corroios and Seixal Jazz.