Gregory was born in Los Angeles, California, where her father was Disney comics writer and artist Bob Gregory. Gregory began her career in 1974 by publishing comics in the all-female Wimmen's Comix anthologies and in other 1970s underground comix, and created the strip Feminist Funnies. In 1976, she published the first issue of a feminist comic book, Dynamite Damsels, which was the first continuing series self published comic by a woman.
In 1990 Gregory created "Bitchy Bitch" Midge McCracken, a woman angry at the world who frequently explodes with rage. She starred in the 40-issue series Naughty Bits, which was published by Fantagraphics from 1991 to 2004. The stories were set in the present day, though they occasionally strayed to such milieus as the Middle Ages. Bitchy Bitch has a lesbian counterpart named Bitchy Butch. Beginning in 2001, a series of shorts featuring Bitchy Bitch called Bitchy Bits was shown on the Oxygen Network animated series X-Chromosome. Life's a Bitch, an animated series spun-off from the X-Chromosome shorts, aired from 2003–2004 on Oxygen in the U.S. and on The Comedy Network in Canada.
Gregory's other work includes the fantasy graphic novel Winging It, the 3-issue series Artistic Licentiousness, and the comic strip Sheila and the Unicorn.