Season 2 is to start production in the fall, with seven new episodes scheduled to start airing in 2009.
Ullman will once again serve as executive producer with her husband Allan McKeown. She will write the episodes as well.
Showtime also said it has ordered a new six-episode comedy series starring Ullman's fellow British comedian Marc Wootton.
"I won't hold it against them that both are from (Britain)," Robert Greenblatt, Showtime's president of entertainment, said in a statement. "But Tracey Ullman is the veteran genius who continues to impress us with her versatility, while Marc Wootton is the up-and-comer who will surprise our audience with his own unique voice. This is an embarrassment of riches for us in the comedy department."