While still a student at the University of Berlin, d'Arrest was party to Johann Gottfried Galle's search for Neptune.

On 23 September 1846, he suggested that a recently drawn chart of the sky, in the region of Urbain Le Verrier's predicted location, could be compared with the current sky to seek the displacement characteristic of a planet, as opposed to a stationary star.

D'Arrest's later work at the Leipzig Observatory led him, in 1851, to the discovery of the comet named for him (formally designated 6P/d'Arrest).

In 1864 D'Arrest made an unsuccessful search for Martian satellites, and posited an upper limit of 70 minutes of arc as the distance from Mars within which a moon should be sought.

[2] He won the Gold Medal of the Royal Astronomical Society in 1875.