During the War of 1812, Roundhead was second-in-command only to Tecumseh among Colonel Henry Procter's British forces. He participated in the Battle of Brownstown on August 5, 1812 and the Battle of Maguaga on August 9. After this battle, Tecumseh presented Roundhead with a sash given to him by General Isaac Brock, as Tecumseh claimed it should belong to an older and more skilled warrior. Roundhead did not wear the honorable sash, as he did not want to cause jealously among the other war chiefs. A few days later, he helped in the capture of Fort Detroit during the Siege of Detroit on August 15. He then joined up with Major Adam Muir for the British occupation of Fort Miami along the Maumee River in September 1812. He later fought in the Siege of Fort Meigs from April 28–May 9, 1813. Another of Roundhead's brothers, Jean-Baptiste, died during this failed siege.