Legia was formed between 5 and 15 March 1916 during military operations in World War I on the Eastern Front in the village of Kostiuchnówka, within the region of Volhynia (Polish: Wołyń).

[9] The first team training began in the spring of 1915 in Piotrków, between 5 and 15 March 1916 – at the request of then Master Sergeant Zygmunt Wasserab (pre-war player of Pogoń Stryj)[10] – who was a part of the Polish Legion's Commanding Staff in Kostiuchnówka in Volhynia to create a football club.

[24][7] These successes were accomplished by strengthening the team by means of conscription to the army[25] of players from such clubs as: Polonia Bytom, Ruch Chorzów, or Wawel Kraków.

[24] At the meeting on 2 July 1957 – chaired by Colonel Edward Potorejko – the club's statute was approved and the first 31-member board of WKS Legia was elected, from which an 11-person presidium was then selected.

[27] Legia players (appearing as a Warsaw team) were invited to Spain to play the first match on the new FC Barcelona stadium, Camp Nou on 24 September.

In the 1962–1963 season with the new league system, the team took the 7th place, and the fight for the Polish Cup again ended at stage eighth-finals (losing to later winner, Zagłębie Sosnowiec, 0–2).

In the game played on 15 August at the Warta Poznań stadium, Legia won after extra time in the final, beating Górnik Zabrze 2–1, with Bernard Blaut scoring in the last minute.

[7] From December 1971 to February 1972, Legia went on a tour of Spain and the countries of South America, including Ecuador, Costa Rica and Colombia – this was the first time the team had visited this part of the world.

Legia in the 1975–76 season finished the league in the middle of the table (8th place), and in the Polish Cup reached the eighth-finals, where they lost to GKS Jastrzębie after penalties.

The team – finishing in 8th position – repeated the result from the previous league season, while in the Polish Cup they were knocked out in the semi-final, losing to Polonia Bytom 1–2.

In addition, the team repeated the result obtained a year earlier in the Polish Cup – Legia reached the semi-final, in which they were knocked out by Zagłębie Sosnowiec after penalties.

During the first meeting in Warsaw, fans, due to the very large number of policemen at the stadium, began to chant the slogans: "Down with communism" and "MO – Gestapo".

Legia finished eighth place in the league table, while in the Polish Cup they fell in the quarterfinals after losing 0–1 against Lech Poznań in Warsaw.

A year later, Legia finished fifth in the fight for the title, and in the Polish Cup reached the 5th round, where they lost against Górnik Zabrze 2–3 after extra time.

[50] Following this, apart from other successful performance in Europe, Legia took 5th place in the league and reached the 5th round of knockout (losing against Wisła Kraków after penalties).

The club's first experience of the Champions League ended in defeat in the qualifying stage – the team fell to Croatian side Hajduk Split (0–1 at home, 0–4 away).

The reason was high ticket prices and the ban on hanging flags and banners on the fence – the conflict ended after three matches in Warsaw thanks to an agreement with activists.

In 1997, the club was transformed into Sportowa Spółka Akcyjna (SSA) Legia Warsaw and a new sponsor was acquired, South Korean company Daewoo.

This season, the legionaries took second place in the league, one reason being a 2–3 loss to Widzew Łódź in the decisive phase of the games (Legia led up until the 85th minute of the match 2–0).

[citation needed] The club played its 100th match in European competitions – the meeting with Macedonian team Vardar Skopje as part of the 1/64 UEFA Cup final ended with Legia's away victory 5–0 on 12 August 1999.

In the UEFA Cup qualifying round, Legia won against Etzella Ettelbruck (4–0 away, 2–1 in Warsaw), and in the next match they defeated IF Elfsborg (4–1 at home, 6–1 in Sweden).

[65] The 2001–02 season, which was led by Dragomir Okuki, ended in Legia's seventh championship title (after a 0–0 draw with Odra Wodzisław in Warsaw),[66] as well as a triumph in the Polish League Cup (3–0 and 1–2 in the final with Wisła Kraków).

[67][68] The next season, 2004–05, the Warsaw team came third in the league table, and in the national cup they lost in the semi-final, falling to Dyskobolia Grodzisk Wielkopolski – 1–1, 1–1, 1–4 on aggregate penalties.

In following competitions, Legia dropped out of the fight for the Polish Cup in the 1/16 finals, falling to fourth-division team Stal Sanok,[73] and in the league they won third place.

[75] At the beginning of the 2007–08 season in Vilnius there were riots caused by Legia fans, which had their apogee at the stadium of FK Vėtra during the match of the second round of the Intertoto Cup.

They finished third place after winning 1–0 against Sporting Lisbon[82] on the last match day in the group stages, sending them to the round of 32 in the 2016–17 UEFA Europa League.

On 28 April 2021, three rounds before the end of the 2020–21 Ekstraklasa season, the players from Łazienkowska won the fifteenth Polish championship, thanks to a goalless draw between Jagiellonia Białystok and Raków Częstochowa.

Legia fans are also vocal with their views on domestic issues, e.g. their conflict with former Polish Prime Minister Donald Tusk, as well as on international politics, e.g. by way of displaying banners reading "Kosovo is Serbian" at the stadium.

[103] On 22 October 2014, when Legia played against the Ukrainian club Metalist Kharkiv they displayed a banner with the names Lwów (Lviv) and Wilno (Vilnius) along with the flag and a prewar coat of arms of Poland on the background, which led to negative reactions.

On 9 April 2022, during an away match against Lech Poznań, Legia fans displayed a banner with an image of Putin hanging from a noose in a Spartak Moscow shirt.