On May 1, 1351, the citizens of Zürich had to swear allegiance before representatives of the cantons of Lucerne, Schwyz, Uri and Unterwalden, the other members of the Swiss Confederacy. Thus, Zürich became the fifth member of the confederacy.

However, Zürich was expelled in 1440 after declaring war on the other states over succession to the territory of Toggenburg. This was known as the Old Zürich War. In 1436, Count Friedrich VII of Toggenburg died without leaving an heir or will. Zürich claimed Toggenburg territory, but so did also Glarus and Schwyz. Zürich occupied the disputed area and cut off the grain supplies to the other two cantons in 1438.

The canton turned to Roman Emperor Frederick III for support. He appealed to Charles VII of France, after Zürich lost the battle of St Jakob an der Sihl in 1443. Charles sent a large army of mercenaries, who faced off against the Swiss confederates in the Battle of St. Jakob an der Birs, near Basel, in 1444. The French suffered heavy losses and had to retreat. Both sides were exhausted by 1446 and reached a truce. Zürich reentered the confederacy in 1450.
 
During the second half of the 15th century, Zürich gained many new territories, including the Thurgau, Eglisau and Winterthur. In addition, it was the presiding canton of the Swiss Diet from 1468 to 1519. This authority was the executive council and lawmaking body of the confederacy, from the Middle Ages until the establishment of the Swiss federal state in 1848.