In 1908, local activist Aleksander Rene was arrested by the Okhrana, and accused of forming an illegal Polish sports organization.

Imprisoned in Łódź, he sent a letter to a Russian Governor, who resided in Piotrków Trybunalski, asking for permission to form a Sosnowiec branch of the Union Sports Club from Sankt Petersburg.

In 1933, Unia Sosnowiec won the league, qualifying to the Ekstraklasa playoffs, where it lost to Naprzód Lipiny.

Among the players of Unia's youth teams was Wieslaw Ociepka, who later became chairman of the Polish Football Association (PZPN).

During World War II, Unia played unofficial, conspirational games against local rivals.

In 1949, after changing its name into Stal Sosnowiec, the team qualified to the Second Division, remaining there until 1954, when it was finally promoted to the Ekstraklasa.

In the 1955 Ekstraklasa, Stal Sosnowiec was a sensation, as it was the runner up, finishing the season in the second spot, only behind CWKS Warsaw.

After promotion, the games of Zagłębie were attended by thousands of people, with the record, 28,000, watching the match against Górnik Zabrze.

After the 1991 season, Zagłębie avoided relegation in the playoffs, in which it beat Jagiellonia Białystok 0–2, 2–0, and 4–2 in the penalty shootout.

In 2001, with a new Italian sponsor ERGOM, Zagłębie planned to win promotion back to the top league.

[1] Note: Flags indicate national team as defined under FIFA eligibility rules; some limited exceptions apply.

Note: Flags indicate national team as defined under FIFA eligibility rules; some limited exceptions apply.

In 1983, American Kent Washington won the Polish Basketball Cup with Zagłębie Sosnowiec.