Random House has acquired a new biography of musical theater legend Stephen Sondheim, to be written by Variety‘s London theater critic David Benedict.

Benedict will wrap up his eight-year tenure at Variety later this week to work full-time on the book, “How Did It Happen: The Life and Career of Stephen Sondheim.” Though not technically an authorized bio (which implies allowing the subject some level of control over what’s included), the book will incorporate the full participation of Sondheim, who’s allowed Benedict unrestricted access to the composer’s personal papers. “How Did It Happen” will be based on extensive interviews with Sondheim as well as information gathered from a wide circle of Sondheim’s friends and collaborators.

Over a long and influential career, the 84-year-old Sondheim has created a canon of works that are known for pushing the musical-theater genre into new realms of intelligence and ambition. Titles on his CV include “West Side Story,” “Gypsy,” “Company,” “Follies,” “Sweeney Todd,” “A Little Night Music,” “Sunday in the Park with George” and “Into the Woods.” Rob Marshall’s movie adaptation of the latter is on tap as a major holiday release this year from Disney.

Benedict and Random House aim to make “How Did It Happen” the definitive biography about Sondheim, previously the subject of Meryle Secrest’s 1998 book “Stephen Sondheim: A Life.” More recently, a two-volume collection of Sondheim’s lyrics were released in 2011 with extensive annotations by Sondheim, and James Lapine, Sondheim’s collaborator on “Sunday in the Park” and “Into the Woods,” directed the doc “Six by Sondheim,” which aired on HBO last year.

Random House vice president and exec editor David Ebershoff picked up the North American rights to the book from the Wylie Agency’s Andrew Wylie. Benedict is expected to deliver his first draft of “How Did It Happen” by December 2017.