Benjamin Henry Latrobe Jr. was born in Baltimore on December 19, 1806, the son of well-known architect Benjamin Henry Latrobe and his wife Mary Elizabeth Hazlehurst. He is best known as a civil engineer who spent most of his career with the Baltimore & Ohio Railroad.

Latrobe spent most of his early life in Washington, DC, where his father was chief architect for the U.S. Capitol building. He and his older brother John studied two years at Georgetown College, leaving in 1817 when the family moved to Baltimore. After the death of his father in 1820, he studied mathematics at St. Mary's College, graduating with high honors in 1824. He studied law at the offices of Baltimore attorney Charles F. Mayer and briefly practiced with his brother. In 1826 he moved to Salem County, New Jersey, where he briefly practiced law, then studied surveying and engineering. He returned to Baltimore in 1829 where his brother John was a junior counsel with the Baltimore & Ohio Railroad. With John's help he got his first job on the railroad in civil engineering starting at the bottom, measuring broken stones for ballasting on the track west of Ellicott's Mills at $1.00 a day. John H. B. Latrobe liked to boast that he and his brother "traded professions." John had been trained as an engineer (at West Point) but became a lawyer, and Benjamin had studied law but became a civil engineer.

Because of his knowledge and skill in the profession Latrobe rose quickly through the ranks. By 1836 his title was Principal Assistant Engineer for the B&O. In the early 1830s he and Chief Engineer Jonathan Knight had surveyed the line for the Washington Branch of the B&O, from Baltimore to Washington, DC. It was Latrobe who designed the massive stone viaduct over the Patapsco River between Baltimore and Howard Counties near Relay. The Thomas Viaduct, named for the first president of the railroad Philip E. Thomas, and built of Patapsco granite, is 612 feet long with eight arches. Its track is 60 feet above the riverbed on a four-degree curve, and at the time of its construction the largest viaduct in North America. It is the oldest multiple-arch railroad bridge in the U.S., and at the present time (2004) is very active, handling freight traffic and commuter trains daily. The Washington Branch opened on August 25, 1835.

Latrobe also designed wooden bridges over the Monocacy River at Frederick Junction, the Patapsco at Elysville (later renamed Daniels) and the Potomac at Harpers Ferry. (Although wooden bridges had a much shorter life span than stone, they were more economical to build. By the 1830s the B&O had to cut costs in its building programs.) The bridge at Harpers Ferry was a particularly difficult engineering feat, having to cross the Potomac and connect the B&O tracks with the existing ones of the Winchester & Potomac Railroad, a line that ran south from Harpers Ferry to Winchester, VA. Latrobe designed a wood truss bridge 830 feet long, consisting of six river spans and a curved span over the C&O Canal on the Maryland side of the river. It contained a single railroad track on the east side and a highway on the west side, and was covered on the sides and top for protection from the weather. This bridge was completed in 1837, and existed until June of 1861 when it was burned during the Civil War.

In the late 1830s Latrobe studied track design at several other northeastern railroads to determine how to update the B&O's line, which had been built mainly with iron strap rail laid on wooden stringers. This method had been fine for the earlier horse-drawn cars and lighter locomotives, but by 1837 the volume of traffic had sharply increased and strap rail was not suited for the heavier locomotives and cars being used. Latrobe recommended the heavier rolled iron "T" rail from England be used to rebuild the "Old Main Line" (the original route) from Baltimore to Harpers Ferry. Because of economic concerns this project was stretched out over a six-year period. In 1838 teams were dispatched by Latrobe to survey the line westward from Harpers Ferry to Cumberland. He set detailed specifications for grading, curvature, bridges, tunnels, and other right-of-way concerns. Whenever he could, Latrobe joined the survey crews on site to supervise. He was one of the first civil engineers to purchase the transit, a surveyor's instrument combining the compass with a pivoting telescope which was much more accurate and easier to use than the old surveyor's compass.

In March 1842, Latrobe became Chief Engineer of the B&O Railroad when Jonathan Knight resigned to return to his home state of Pennsylvania to enter politics. By November of that year the line to Cumberland had been completed. Under Latrobe's supervision the line westward over the Allegheny Mountains and through northwestern Virginia (now West Virginia) was surveyed and built, finally reaching the Ohio River at Wheeling on December 24, 1852. The original goal of the founders of the Baltimore & Ohio Railroad-to connect the port city of Baltimore with river traffic on the Ohio-had finally been met. In his later years Latrobe served as a consultant on various engineering projects, including the Hoosac Tunnel (a 4.75 mile railroad tunnel in Massachusetts built 1852-73), and John Roebling's 1869 design for the Brooklyn Bridge. For many years he served as president of the Pittsburgh and Connellsville Railroad, a B&O-controlled line in western Pennsylvania opened in 1871.

March 12, 1833. They had six children, five living to adulthood. Benjamin H. Latrobe, Jr., died on October 19, 1878, in Baltimore.