Excavations have shown that the area around Sulęcin was inhabited already in the 2nd century BC. The city developed from a Slavonian settlement and was mentioned for the first time in documents in 1241. Until 12th century under dominion of he Silesian line of the Piast dynasty, the town with 10 surrounding villages was handed over by Henry I the Bearded to Mroczko from Pogorzela, who in 1244 gave it to the Knights Templar. In 1249 Sulęcin became a part of March of Brandenburg. In 1269 Otto, the Margrave of Brandenburg ordered to build a castle in the town. After disbanding of the Knihts Templar Order by Pope Clement V in 1312 Sulęcin was ruled by the Knights Hospitaller. They leased the city in 1318 to the Brandenburg Margrave Woldemar. Eight years later the city was reclaimed by the Knights Hospitaller Order and stayed under their supremacy until 1810.
In 1419 Sulęcin suffered a severe damage, as the Hussite Wars reached the city. In 1733 Frederick William I, King of Prussia visited the town. As a result of the new Prussian district division of 1818 a new district Landkreis Sternberg was established. Sulęcin was the capital of it until 1852. In 1873 Sternberg was divided into Landkreis Oststernberg with Sulęcin as a capital and Landkreis Weststernberg. At that time the city's industry was based on textile production and mills. In the middle of 19th century number of inhabitants reached 4500. After the discovery of lignite in the vicinity of the city a briquette factory was set up in Sulęcin. This led to the development of infrastructure and resulted in an increase of the population to 5769 inhabitants in 1885. After the World War I a number of companies involved in timber processing set up in the town. The number of residents in 1939 according to the last German census was 5867.
Main square view on postcard, 1905
On 2 May 1945 Sulęcin was taken by the Red Army. Although there was no resistance, the houses in the city center were plundured by the soldiers and set on fire. As a result around 50% of Sulęcin was completely destroyed and the ethnic German population was expelled. After the World War II Sulęcin became a part of Poland. In years 1945 - 1975 it was a capital of a county.