Lumley is especially noted for his actions at the Battle of Antrim where he saved the lives of several magistrates and was seriously wounded fighting when leading a cavalry charge against[1] the United Irishmen rebels in the Irish Rebellion of 1798.

The initial rebel attack was beaten back and Lumley's cavalry troops attempted to rout them with a charge whilst the remainder of the garrison retreated into the castle.

[2] Two years after the rebellion Lumley had recovered from his wounds and led his regiment in General Abercromby's invasion of Egypt in 1801 and helped force the French army there to surrender, although it is not clear which actions he participated in.

Lumley fought at the Battle of Blaauwberg which finalised the British capture of the colony and the following year joined General Whitelocke's force which unilaterally invaded the River Plate.

Lumley was not deemed responsible for the operation's failure and in 1808 was attached as commander of the light cavalry brigade in a small British army which landed in Sicily and then invaded Italy under Sir John Stuart.

In 1819, Lumley was made Governor of Bermuda and retained the position until 1825 but departed under a cloud after being convicted in court of illegally interfering in the ecclesiastical matters of the island and fined £1,000 (equivalent to £104,000 in 2023).