Neighbouring provinces are (from the south clockwise) Phetchaburi, Ratchaburi and Samut Sakhon. Local people call Samut Songkhram Mae Klong. The province is the smallest of all Thai provinces areawise. Chang and Eng Bunker, the famous Siamese twins were born here.

The word "samut" originates from the Sanskrit word समुद्र samudra meaning "ocean", and the word "songkhram" from Sanskrit सङ्ग्राम saṅgrāmḥa meaning "war". Hence the name of the province literally means "war ocean".

Samut Songkhram is at the mouth of the Mae Klong river to the Gulf of Thailand. With several canals (khlong) the water of the river is spread through the province for irrigation. At the coast are many lakes for producing sea salt. The sandbar Don Hoi Lot at the mouth of the river is famous for its endemic shell population of Solen regularis.

In the Ayutthaya period the area of Samut Songkhram was known as "suan nok" (Thai สวนนอก, "outer garden") and was administered by Ratchaburi. During the reign of King Taksin it was made a province. It was the birthplace of Queen Amarindra of King Rama I. The birthplace of King Rama II in Amphawa district is now a memorial park.

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