Born in County Cook, Ireland. At the age of twelve, he followed his widowed mother to America, eventually settling in New York City. There he worked for a law publisher and about 1843, he joined a military company known as the Baxter Blues. This unit fought in the Mexican War with Sweeny as its 2nd Lieutenant. He was wounded and his right arm was amputated, but by 1848, he had recuperated sufficiently to accept a Lieutenant's commission in the 2nd U.S. Infantry. In that regiment, he fought Indians in the Southwest and on the Great Plains until the start of the Civil War.

In May, 1861, he became Brigadier General of Missouri's short time volunteers. Three months later, he fought under Brigadier General Nathaniel Lyon at Wilson's Creek, where he fell wounded and was carried from the field. Within days, he was mustered out of volunteer service, but re-entered it the following January as Colonel of the 52nd Illinois Infantry. He led the outfit at Fort Donelson and expertly commanded a brigade at Shiloh where he was wounded again; he was also wounded at Corinth. On March 16, 1863, he was raised to Brigadier General of Volunteers and by the outset of the Atlanta Campaign, he was leading a division in Major General Grenville M. Dodge's XVI Corps of the Army of Tennessee.

In the early part of the campaign, Sweeny distinguished himself at Shiloh, Corinth, Kennesaw Mountain, and in the Battle of Atlanta. On July 25, 1864, he brought to a climax a long-lived feud with Dodge and another political commander he resented -- Brigadier General John W. Fuller. Entertaining both officers at his headquarters (supposedly while under the influence of liquor), Sweeny called Dodge a "God d----- liar" and a "cowardly son of a bitch," struck him, and then wrestled his fellow divisional leader Fuller to the ground. Dodge at once arrested his assailant on numerous charges, including conduct unbecoming an officer, but in January 1865, a military court acquitted him.

Sweeny remained in the army until May, 1870 despite controversial service that included active participation in the Fenian movement. In the summer of 1866, he led a force of Irish Americans in an effort to capture Canada from the British. Thwarted by U.S. officials, he was arrested but later released. After his retirement as a Brigadier General of Regulars, he lived in Astoria, Long Island, New York, until his death on April 10, 1892.

Also:

The Not as Famous: Gen. Joseph Finegan

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