Thomas de Beauchamp, 12th Earl of Warwick (March 16, 1338/9 – 1401) was an English nobleman, and one of the primary opponents of Richard II.

He was the son of Thomas de Beauchamp, 11th Earl of Warwick and Catherine Mortimer, a daughter of the 1st Earl of March, and succeeded his father in 1369.

The earl accompanied John of Gaunt in campaigns in France in 1373, and around that time was made a Knight of the Garter. In the parliamnets of 1376 and 1377 he was one of those appointed to supervise reform of Richard II's government. When these were not as effective as hoped, Beauchamp was made governor over the king. He brought a large contingent of soldiers and archers to Richard's Scottish campaign of 1385.

In 1387 he was one of the Lords Appellant, who endeavored to separate Richard from his favorites. After Richard regained power, Beauchamp retired to his estates, but was charged with high treason in 1397, supposedly as a part of the Earl of Arundel's alleged conspiracy. He was imprisoned in the Tower of London (in what is now known as the "Beauchamp Tower"), pleaded guilty and threw himself on the mercy of the king. He forfeited his estates and titles, and was sentenced to life imprisonment on the Isle of Man. The next year, however, he was moved back to the Tower, until he was released in August 1399 after Henry Bolingbroke's initial victories over king Richard II.

After Bolingbroke deposed Richard and became king as Henry IV, Beauchamp was restored to his titles and estates. He was one of those who urged the king to execute Richard, and accompanied Henry against the rebellion of 1400.

Beauchamp died in 1401 (sources differ as to whether on April 8 or August 8). He had married Margaret, daughter of the 3rd Lord Ferrers of Groby, and was succeeded by their son Richard de Beauchamp, 13th Earl of Warwick.