Noted for their sharp dialogue and fine character development, the Spenser books carry on a tradition while updating it, particularly in giving its hero two strong alter egos in Hawk, a black friend and right-hand man; and Susan Silverman, Spenser's psychologist love interest. Parker's inclusion of other races and sexual persuasions (several of his novels feature gay characters, a sensibility strengthened in Parker through his sons, both of whom are gay) give a more modern feel to the cases coming into Spenser's office.

The Spenser series, which began with 1973's The Godwulf Manuscript, has an element of toughness that suits its Boston milieu; but it delves just as often into the complex relationship between Silverman and Spenser, and the interplay between the P.I. and Hawk.

By the late `80s, Parker had acquired such a reputation that the agent for Raymond Chandler's estate tapped him to finish the legend's last book, Poodle Springs. It was a thankless mission bound to earn criticism, but Parker carried off the task well, thanks to his gift for to-the-point writing and deft plotting. "Parker isn't, even here, the writer Chandler was, but he's not a sentimentalist, and he darkens and deepens Marlowe," the Atlantic concluded. In 1991, Parker took a second crack at Chandler with the Big Sleep sequel Perchance to Dream.

Parker took other detours from Spenser over the years. In 1999, Family Honor introduced Sunny Randall, a female Boston private eye Parker created with actress Helen Hunt in mind. Two years earlier, he introduced L.A.-to-New England cop transplant Jesse Stone in Night Passage. He also authored four bestselling Westerns featuring Virgil Cole and Everett Hitch, a few young adult books, as well as several stand-alone novels that were well-received by his many fans.

Parker died suddenly in January 2010 while at home at his desk, working on a book. The cause was a heart attack. He was seventy-seven.