Moffat, who also oversees Doctor Who, was honoured with the special award for outstanding writing.
Accepting the award, he told the London ceremony: "Write what you love. I've never loved anything as much as Doctor Who and Sherlock."
However he and Sherlock co-creator Mark Gatiss lost out to ITV1's Appropriate Adult for best TV short-form drama.
Screenwriter Neil McKay's Fred West drama also beat This is England '88 writers Shane Meadows and Jack Thorne to the prize.
Starring Dominic West, Appropriate Adult has already been honoured with TV Baftas, RTS and Broadcasting Guild Awards.
BBC3's Being Human won the Writers' Guild award for TV drama series, while Hollyoaks writer Nick Leather won best continuing TV drama.
BBC4 comedy Holy Flying Circus, written by Tony Roche, won best TV comedy.
Doctor Who spin-off The Sarah Jane Adventures, written by Phil Ford, took the prize for best children's TV script for its episode The Curse of Clyde Langer.
Other winners included Dexter Fletcher's directorial debut Wild Bill, which won best first feature film for him and co-writer Danny King.
We Need to Talk About Kevin won best screenplay for Lynne Ramsay and Rory Stewart Kinnear.
The awards were handed out in London on Wednesday night by The Writers' Guild of Great Britain, which supports writers across every media, from books, theatre, TV and radio.
Rachel De-lahay won best play for The Westbridge, a Royal Court production that ran at Peckham's Bussey Building, while best play for children and young people went to Brendan Murray for Hare and Tortoise.
There were also two awards for radio writing, with Radio 4's Pandemic, by John Dryden, winning the drama category and Matt Berry's I, Regress winning best radio comedy.
Best fiction book went to Patrick McGuinness' The Last Hundred Days, and best videogame script was won by Paul Crocker's Batman: Arkham City.
Sherlock creator Steven Moffat has been handed the top prize at this year's Writers' Guild Awards.