ITV controller Peter Fincham admitted the show, which starred Ian McKellen and Derek Jacobi as a sharp-tongued gay couple, got "mixed reviews".
Speaking at the Edinburgh television festival, he said: "Not everyone liked Vicious, but many people did and that critical tide turned considerably during the run."
He said the show was "bold" and would "evolve", adding that he did not want to "commit the first and most obvious sin" of dropping a show if it had disappointing ratings.
Inbetweeners star Blake Harrison will appear in a new comedy set in a Margate bed and breakfast.
Mr Fincham said The Job Lot, which is set in a job centre, would return for another series but move to ITV2.
There will also be a new series of the Ancient Rome sitcom Plebs on ITV2.
Other new shows announced today include Pat And Cabbage which stars Barbara Flynn and Cherie Lunghi as newly single friends.