Martin Gilbert, the official biographer of Winston Churchill, who also wrote histories of many of the signal events of the 20th century, including both world wars, the Holocaust and the Middle East conflict, died on Tuesday in London. He was 78.

His death was announced on the floor of Parliament. Mr. Gilbert, an appointee to the parliamentary committee investigating Britain’s involvement in the Iraq war, had been in declining health since suffering a heart arrhythmia several years ago.

Mr. Gilbert, whose work was translated into many languages, was one of the world’s most prolific historians. He was the author of almost 90 books, the most famous of which was the compendious Churchill biography begun in the 1960s by Churchill’s son, Randolph.

Often described as the longest biography ever published, the work spans eight volumes and more than eight million words. Mr. Gilbert, who assumed the project after Randolph Churchill’s death in 1968, wrote the last six volumes, which take Winston Churchill from 1917 to his death in 1965.