Margaret Blackwell was a 24th century Starfleet admiral.

In 2370, she ordered the USS Enterprise-D to rendezvous with the USS Crazy Horse, but did not discuss further details via subspace. After having picked up Admiral Erik Pressman from the Crazy Horse to search for the USS Pegasus, Captain Jean-Luc Picard got suspicious about the true nature of the mission and again contacted Blackwell, whom he knew on a first-name basis, to get more information. She refused, instead advising Picard to follow Pressman as the chief of Starfleet Intelligence was behind him. (TNG: "The Pegasus")