Up until about two decades ago, Library of Congress Subject Headings allowed for the sub-heading "Biography" to be placed after an author's name (as a subject) to lead to books that were primarily biographical in nature. Today, books that are primariliy biographical are cataloged under the name of the subject with no further words. Unfortunately, for really major authors, there may be over 100 books under the undivided heading for their names. You may wish to consult with your professors or colleagues as to which biography(ies) of an author they recommend.
Oxford Dictionary of National Biography The Oxford DNB is the national record of men and women who have shaped British history and culture, worldwide, from the Romans to the 21st century. The Dictionary offers concise, up-to-date biographies written by named, specialist authors. It is overseen by academic editors at Oxford University, UK, and published by Oxford University Press. "British" is defined to include anyone who lived under British colonial rule, so it includes many men and women who lived all or most of their lives in pre-Revolutionary America, India, Africa, and other former British colonies.
Literature Resource Center. LRC contains articles that were originally commissioned for several print reference sources published by Gale Research Co., such as the Dictionary of Literary Biography, as well as articles from sources that Gale has licensed from other publishers, including the excellent lengthy essays originally published by Scribners as American Writers, British Writers, and World Writers. The default search is by author, but it is searchable by literary titles or keywords as well. Some of the documents are entirely biographical in nature, but others are works of criticism and many are a combination of both biography, criticism, and bibliographical references. An excellent place to start for information on most world writers. A search on William Faulkner, limiting the results to the "Biography" tab, links to essays on him in 5 different volumes of DLB, both editions of the essays in American Writers, and a briefer summary in Contemporary Authors.
Biography Reference Bank. This resource contains full texts of many of the biographical reference books published by one of the most distinguished reference publishers of the 20th and early 21st centuries, the H.W. Wilson Company, in addition to references (and some full text) of hundreds of other articles. For example, a search on D. H. Lawrence as a subject produces almost 600 citations, including links to the articles in Chambers' Biographical Dictionary, World Authors 1900-1950, and the Hutchinson Encyclopedia of Biography. Many of the results, however, are to critical rather than biographical articles.
American National Biography. Detailed articles on more than 18,000 men and women, from all eras and walks of life, whose lives have shaped the United States. Includes bibliographies and links to web resources. Several hundred new entries added each year.
Wikipedia. For strictly biographical information, Wikipedia may be a realiable source of information, although remember that anyone with a grudge or a biased perspective on a person, or any topic, may write or edit Wikipedia entries. It may be reliable in terms of recommending which full-length biography(ies) of the subject are the most reputable or up-to-date.
Oxford Reference Center. Over 150 dictionaries, handbooks, and encyclopedias from Oxford University Press, which may be searched in their entirety, within individual volumes, or within groups of volumes by subject, many of which include biographical information.
Allibone, Samuel Austin A Critical Dictionary of English Literature and British and American Authors, Living and Deceased, From the Earliest Accounts to the Latter Half of the Nineteenth Century. Philadelphia: J.B. Lippincott, 1858-71. 3 vols. The link is to the Making of America (MoA) collection of Ebooks.
Something About the Author. This source examines the lives and works of authors and illustrators for children and young adults and is the preeminent source on authors and literature for young people.