Representative from Maryland and mayor of Baltimore.
Hillen was born at the family estate, "Hillendale," on Hillen Road north of Baltimore City.
He graduated from Georgetown College, studied law, was admitted to the bar, and commenced practice in Baltimore.
He served as member of the Maryland House of Delegates from 1834 to 1838.
Hillen was elected as a Democrat to the Twenty-sixth Congress (March 4, 1839 – March 3, 1841).
Afterward he resumed the practice of law and served as mayor of Baltimore from 1842 to 1845.
He died in New York City, and is interred in Greenmount Cemetery in Baltimore.
His wife was a daughter of General Columbus O'Donnell.