Charles was born in Brunswick, the eldest son of Frederick William, Duke of Brunswick-Lüneburg. After the death of his father in 1815, Charles inherited the Duchy, but since he was still underage, he was put under the guardianship of George, the Prince Regent of the United Kingdom and Hanover. When Charles neared his 18th birthday, a dispute over the date of his majority erupted; Charles claimed majority at age 18, while George considered the age of majority to be 21 years. A compromise was made, and Charles reached his majority at age 19, and took over government on 30 October 1823.

In 1827, Charles declared some of the laws made during his minority invalid, which caused a dispute with Hanover. The German Confederation finally had to intervene in this conflict and ordered Charles to accept all the laws from his minority, which he did.

Charles' administration was considered corrupt and misguided. When in 1830 the July Revolution broke out, Charles happened to be in Paris; he fled home to Brunswick, where he announced his intention to suppress all revolutionary tendencies by force of arms. But on 6 September, he was attacked by stone throwers while riding home from the theater; on the next day, a large mob tried to break into the palace. Charles fled; the palace was completely destroyed by fire. When Charles' brother, William, arrived in Brunswick on 10 September, he was received joyfully by the people. William originally considered himself only his brother's regent, but after a year declared himself ruling duke. Charles made several desperate attempts to depose his brother by diplomacy and by force, but they were unsuccessful. None of the other European monarchs wanted to support Charles.

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