The 27-year-old arrives in a loan deal that will see him join the club until January 25 to further boost Brian McDermott's striking options.
Blackstock, who has scored 83 career goals in 306 appearances, brings a wealth of experience, having also featured heavily for Southampton and QPR, and is a player that the United manager knows well.
The boss said on the official Leeds United website: “I’ve known Dexter for a long time, being brought up in Oxford. I’m really pleased we’ve managed to secure his services.
"He’s a really good age for a striker and I’m sure he has many good years in front of him. We are all really looking forward to working with him.”
The striker is likely to go straight into the squad for Saturday’s trip to Huddersfield Town.
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