Dunlop was born in Georgetown, which at that time was in that portion of the State of Maryland ceded to the federal government pursuant to the Residence Act of 1790 but which remained under the jurisdiction of Maryland until the enactment of the District of Columbia Organic Act of 1801.

He received an Artium Baccalaureus degree in 1811 from the College of New Jersey (now Princeton University) and read law.

[1] Dunlop received a recess appointment from President James K. Polk on October 3, 1845, to a Judge seat on the United States Circuit Court of the District of Columbia vacated by Judge Buckner Thruston.

His service terminated on November 27, 1855, due to his elevation to be Chief Judge of the same court.

[1] Dunlop received a recess appointment from President Franklin Pierce on November 27, 1855, to the Chief Judge seat on the United States Circuit Court of the District of Columbia vacated by Chief Judge William Cranch.