L. McGarry was a Starfleet officer assigned to the starship USS Voyager, a lieutenant commander who was killed in the line of duty sometime before 2377. McGarry's name was read out on a casualty report of all who died during that vessel's journey through the Delta Quadrant. (VOY: "Imperfection")

This character was only mentioned in writing.
Judging by the lieutenant commander rank, it is possible this name refers to one of the senior officers killed en route when Voyager was dragged to the Delta Quadrant, perhaps the chief engineer or the unnamed chief medical officer played by Jeff McCarthy.
As with many names on the "Imperfection" list, Leo McGarry is an in-joke referring to the character on The West Wing.
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