The 31-year old has penned a two-year deal with the American club after being released from his contract with Qatari club Al-Rayyan.
DC attempted to sign the three times capped Australian international three seasons ago and finally got their man.
Allsopp was reportedly on the verge of returning to the Victory but decided he could not pass up the opportunity to play in MLS with DC United – the club former Victory championship-winning midfielder Fred joined after his stint in Melbourne although he recently left the club.
DC United general manager Dave Kasper said the signing of Allsopp was a positive move.
“He's an athletic forward with a nose for the goal who will complement our other attacking players," Kasper said.