Sulęcin is located in the north-western part of the Lubuskie Province, in the Postomia River Valley. It developed from an old Slavic settlement located at a trade route leading from Poznań to Lubusz. Following the feudal fragmentation of Poland in 1138, Sulęcin together with the entire Lubuskie Land remained the possession of the Silesian princes. The oldest surviving document concerning Sulęcin dates back to 1241 when a Silesian magnate, Mroczko of Pogorzela obtained consent to settle German colonists in Sulęcin. Three years later (in 1244), motivated religiously or by the fiasco of the colonization, he gave the town and 10 villages to the Templar Knights. At that time, the importance of Sulęcin grew: the Sulęcin castle was built, and the cloth makers were brought here - their craftsmanship made the town famous in the next centuries. The people of Sulęcin traditionally dealt with farming, craft, brewery and cloth making. In 1250 Prince Bolesław Rogatka sold the Lubuskie Land with Sulęcin to the Brandenburg margraves. After the House of Ascania had died out, the land was taken over by the Witellsbachs. Until 1945 Sulęcin's history was connected with the Brandenburgian, Prussian and German state community. Another important mention comes from 1269, when the army of Bolesław the Pious, Prince of Greater Poland, destroyed the castle in Sulęcin in retaliation for the Brandenburgian invasion. After the dissolution of the Templar Knights Order and following some disputes with the Brandenburgian margraves and the Wittelsbachs, in 1350 the town and its surroundings became the property of the Order of St. John and belonged to them until 1810. Around 1375 the town fortifications were built. That was when the castle disappeared from the pages of history. In 1563 the House of the Order of St. John was built in Sulęcin, and in 1591 - the first school. The town hall was also built in this century.
In 1574 the magnates and clergy of Greater Poland welcomed the first election king of Poland, Henry of Valois, in Sulęcin, and in 1657 hetman Stefan Czarniecki's army marching to Denmark filed past Sulęcin. At the turn of November and December 1689 King Jan III Sobieski's daughter, Teresa Kunegunda, stayed in Sulęcin. In 1733 the Prussian King Frederick William I visited the town. In the years 1714 – 1722 a company of the Prussian army was stationed in the town.
Sulęcin was also hit by numerous disasters, e.g. plagues in every century, fires, the Thirty Years' War. It was destroyed again by the Russian army stationed here during the Seven Years' War, fighting with Frederick II.
In the years 1806 – 1812 the town was controlled by the Napoleonic army. This was the end of the commandery of the Order of St. John in Łagów (1810). From then until 1852 Sulęcin was the capital of the Torzymski District. From 1873 Sulęcin was the seat of the authorities of the Eastern Torzymski District.
In the second half of the 19th century timber industry plants appeared in Sulęcin. Peat and lignite were mined in the area. Factories were established in the town: a briquette factory, O. Franke's train carriage factory, Karl Kaiser's electrical engine factory. By the end of the 19th century a railway line was built there. Before World War II, Sulęcin developed mainly due to its timber industry. It had a population of 6.500 then.
In 1851 the new town hall was built. Sometime later - the seat of the district authorities and the court were built. In 1858 the monks from the Order of St. John founded a hospital in the town; its older part dating back to 1899 was rebuilt in 1931. Buildings for the army administration were also built in Sulęcin. In the interwar period there were many restaurants, cafes and pubs in the town. A sport and recreation centre was founded by Karl Kaiser on Winna Góra.
The outbreak of the war changed the image of Sulęcin forever. After World War II, Sulęcin and the previous Eastern Torzymski District were within the boundaries of Poland. A new period in the town's history began. On 2 February 1945 Sulęcin was taken by the Red Army troops. Although there was no direct fighting, war damage in Sulęcin was estimated at 40%, as the town was ravaged. The church, town hall, district authorities' building, train station and many houses were destroyed by fires. On 24 June 1945 displacement of the German population beyond the Oder River began. The last German inhabitants were displaced in 1950. Repatriates from beyond the Bug River and many displaced inhabitants from the Poznań Province started arriving to Sulęcin. One of the first signs of normalization of the social and economic life in the town was the establishment of Polish administration there. In the years 1945 – 1975, just like before the war, Sulęcin was the seat of the district authorities within the Zielonogórskie Province.
Some outstanding persons come from Sulęcin. Reinhold Heidenstein, the author of "Moscow War", the poetess Marta Renata Fischer and Ernst Krause (known as Carus Stern), a journalist and scholar, who popularized Charles Darwin's theory of evolution, were born here.