The show, which stars three-time Emmy Award winner Edie Falco in the title role, is a co-production of Lionsgate and Showtime. It premiered on Monday.
Production of the second season's 12 episodes begins this summer in New York.
"We're delighted about Showtime's early pickup of 'Nurse Jackie' and the terrific response the premiere has received," Kevin Beggs, president of Lionsgate Television Programming and Production, and Sandra Stern, executive vice president and chief operating officer of Lionsgate Television, said in a joint statement issued Wednesday. "It's a testament to the brilliant work of Edie Falco and the extraordinary supporting cast and creative team. Showtime has been a great partner on both 'Nurse Jackie' and 'Weeds' and we look forward to extending and expanding our relationship in the years to come."