After finishing schooling, Carroll worked as a student lawyer for the law office of Brown and Brune in Baltimore. He was admitted to the bar in 1851. Carroll practiced law in Maryland from 1854 until 1858. He ran as a Howard County Democratic candidate for the state General Assembly in 1854,, however losing to his opponent from the newly-dominant "Know Nothing" Party during the political crises of the 1850s. Carroll then moved to New York City and while there, accepted a position as deputy clerk and United States Commissioner in the office of the clerk of the United States District Court. He stayed there until 1861, at the outbreak of the Civil War, when he returned to Maryland, where he then remained the rest of his life. When he returned to Maryland, Carroll purchased the "Doughoregan Manor", historic family estate in Howard County, near Ellicott City from his older brother Charles Carroll. Carroll was elected into the Maryland State Senate of the General Assembly of Maryland in 1867 and served two terms. He was elected President of the State Senate in 1874. In 1875, Carroll became the Democratic Party nominee for Governor of Maryland, opposed by James Morrison Harris. He won by a 10,000-vote majority and was inaugurated as governor on January 12, 1876.
Strikes and unrest in 1877
The Great Railroad Strike of 1877 began with a sudden cut in wages by the B. & O. Railroad's Board of Directors and President John Work Garrett, which caused workers to walk off the job in Martinsburg, West Virginia, and spread nationwide to the rest of the B. & O., as well as several other lines. Governor Carroll called up the 5th and 6th Regiments of the Maryland National Guard to stop railroad workers from striking in Cumberland, Hagerstown and in Frederick County's shops and roundhouses at Brunswick. Once the news spread by telegraph east, it touched off riots in Baltimore at the Mount Clare Shops and the yards at the B. & O.'s Camden Street Station, headquarters of the line. The National Guard attempted to march from their armories to Camden Station—the Fifth Regiment from the armory in the assembly hall above the Richmond Market along North Howard Street in the northwest city, and the Sixth from their armory at North Front and East Fayette Streets, near Jonestown/Old Town. The Fifth marched south down Howard Street and the Sixth attempted to march south on Front Street along the east bank of the Jones Falls for a few blocks then west on East Baltimore Street, through the middle of the downtown business district. Despite this precaution, each regiment had to again literally fight its way through the streets of the city, attacked by projectiles, rocks and angry mobs the entire way. Conflict gripped the city and Governor Carroll was powerless to stem the tide. Later, additional reinforcements of Federal troops were called in by newly elected 18th President Rutherford B. Hayes to restore order in Baltimore.
Mary Helen Carroll ; married Herbert Robbins, no issue
Carroll was married secondly to Mary Carter Thompson, daughter of Judge Lucas P. Thompson, in April 1877 and had one son. As of 2012, Philip's grandchildren owned Doughoregan Manor, the family estate in Howard County.
Philip Acosta Carroll ; married to Nina Ryan, 2 sons and 1 daughter
Mary Thompson's sister Caroline Thompson was married to John Lee's older brother, Charles Carroll. Carroll died in Washington, D.C. and was buried at the New Cathedral Cemetery in Baltimore City, Maryland.
