The route is a major conduit on the western and northern sides of Gaithersburg, where the highway serves the National Institute of Standards and Technology and the former Lakeforest Mall and connects with Interstate 270 (I-270) and MD 355.

MD 124 continues north past the Montgomery County Airpark, beyond which the route changes from a four- to six-lane divided highway to a two-lane undivided road as it passes west of Laytonsville on its way to Damascus.

MD 124 was built from Laytonsville south to Redland by 1910 and constructed from Gaithersburg to its southern end in the early 1910s.

MD 124 begins as Quince Orchard Road at an intersection with MD 28 (Darnestown Road) northeast of Quince Orchard High School in Darnestown, just southwest of the southwestern corner of the city of Gaithersburg.

Quince Orchard Road heads south as a county highway into North Potomac.

North of the railroad crossing, MD 124 has a partial cloverleaf interchange with I-270 (Eisenhower Memorial Highway), with a park and ride lot serving MTA Maryland commuter buses located in the southwest quadrant of the interchange.

The highway expands to a four-lane divided highway again between Flower Hill Way—which leads to Washington Grove Lane, which leads to the town of Washington Grove—and MD 115 (Muncaster Mill Road) on the western edge of Redland.

MD 124 continues as a four-lane undivided highway through an industrial area surrounding the Montgomery County Airpark.

MD 124 passes through the hamlet of Woodfield and parallels the Magruder Branch of Great Seneca Creek into the unincorporated community of Damascus.

The highway reaches its northern terminus on the eastern edge of downtown Damascus at an intersection with MD 108 (Main Street).

[6][7] The continuation of the highway along West Diamond Avenue to Frederick Road in Gaithersburg was completed in 1914.

[8][9] The gap between Great Seneca Creek and Woodfield was filled between 1931 and 1933; the highway was signed as MD 124 in the latter year when it was completed.

[28] MD 124 was expanded to a four-lane divided highway from I-270 south to Long Draft Road in 1987.

[29][33] The ramp from southbound I-270 to northbound MD 124 was removed in favor of a traffic signal–controlled left turn in 2004.