Monson was born on August 21, 1927 at St. Mark's Hospital in Salt Lake City, Utah, the son of George Spencer Monson (1901–1979) and Gladys Condie Monson (1902–1973). His Swedish paternal grandfather, Nels Monson, was born in Torhamn before coming to Utah at the age of 16. The second of six children, Monson grew up in a "tight-knit" family, with many of his mother's relatives living on the same street and the extended family frequently vacationing together. The family's neighborhood included several residents of Mexican descent, an environment in which Monson said he developed a love for the Mexican people and culture. Monson often spent weekends with relatives on their farms in Granger (now part of West Valley City), and as a teenager, he worked at a printing Business his father managed.

From 1940 to 1944, Monson attended West High School in Salt Lake City. In the fall of 1944, he enrolled at the University of Utah. Around this time he met his Future wife, Frances, whose family came from a higher social class on the east side of the city. Her father, Franz Johnson, saw an immediate connection because Monson's great uncle, Elias Monson, had baptized him into the LDS Church in Sweden.

In 1945, Monson joined the United States Naval Reserve and anticipated participating in World War II in the Pacific theater. He was sent to San Diego, California, for training, but was not stationed overseas before the end of the war. His tour of duty lasted six months beyond the end of the war, then he returned to the University of Utah. Monson graduated cum laude in 1948 with a bachelor's degree in Business management. Monson did not serve a mission as a youth. At age 21, on October 7, 1948, he married Frances Beverly Johnson in the Salt Lake Temple. The couple eventually had three children: Thomas Lee, Ann Frances, and Clark Spencer.

In the mid-1950s Monson was the secretary of the Utah State Roller Club, a group of pigeon breeders. Monson was a member of the National Executive Board of Boy Scouts of America starting in 1969. From 1969 to 1988 Monson was on the Mountain Bell Board of Advisors. From 1971 to 1977, he served on the Utah State Board of Higher Education and the Utah State Board of Regents. He was a member of the board of Directors of Commercial Security Bank, chairing the bank's audit committee for 20 years. In 1993, when the bank was purchased by Key Bank, Monson joined the Board of Directors of Key Bank. In 1981, Ronald Reagan appointed him to the President's Task Force on Private Sector Initiatives, serving until its completion in December 1982.

Monson briefly taught at the University of Utah, then began a career in publishing. His first job was with the Deseret News, where he became an advertising executive. He joined the advertising operations at the Newspaper Agency Corporation at its formation in 1952. One year later, Monson transferred to the Deseret News Press, beginning as sales manager and eventually becoming general manager. While at Deseret News Press, Monson worked to publish LeGrand Richards's A Marvelous Work And A Wonder. He also worked with Gordon B. Hinckley, the LDS Church's representative on publications, with whom he would later serve in the First Presidency.

On 16 June 1955, at age 27, Monson became a counselor to Percy K. Fetzer in the presidency of the Salt Lake Temple View Stake. He was replaced as bishop of the 6th-7th ward the following month. In the stake presidency, Monson oversaw the stake's Primary, Sunday School, MIA, athletics and budget, until he was moved to Holladay, Utah, in June 1957. In Holladay, Monson was assigned to a ward building committee, to coordinate ward members' volunteer Service to build a meetinghouse.

In April 1959, at age 31, Monson became President of the church's Canadian Mission (consisting of Ontario and Quebec), and served until January 1962. Monson's third child, Clark, was born during his mission presidency.

Efforts made during Monson's Service came to fruition when a stake was organized in Toronto on August 14, 1960. However, most of the mission's area remained in districts. A more complete presence in Ontario would not come until the dedication of the Toronto Ontario Temple in 1990, which Monson attended as a member of the First Presidency.

Monson was sustained to the Quorum of the Twelve Apostles at general conference on October 4, 1963. He was the youngest man called to the Quorum of the Twelve in 53 years, and was 17 years younger than the next youngest member, Gordon B. Hinckley. He was ordained and set apart on October 10, 1963, by Joseph Fielding Smith.

From 1965 to 1968, Monson oversaw church operations in the South Pacific and Australia. During this time he organized the first LDS stake in Tonga.

In 1966, Monson was honored as a distinguished alumnus by the University of Utah. His first honorary degree, an Honorary Doctorate of Laws, was conferred in April 1981 by Brigham Young University. He received a Doctor of Humane Letters from Salt Lake Community College in June 1996, an Honorary Doctor of Business from the University of Utah in May 2007, and an honorary doctorate degree in Humanities from Dixie State College in May 2011.

He was President of the Printing Industry of Utah and a former board member of the Printing Industries of America. A Life Scout and Explorer crew member in his youth, Monson served in several adult Scouting leadership capacities: merit badge counselor, member of the Canadian LDS Scouting Committee, chaplain at a Canadian Jamboree, and a member of the General Scouting Committee of the LDS Church. He was also a proponent of the Scouting for Food drive, and he served on the national executive board of the Boy Scouts of America from 1969 to his death. He also represented the Boy Scouts of America as a delegate to the World Conferences in Tokyo, Nairobi, and Copenhagen.

With his Business background, he helped oversee many church operations, including KSL Newsradio and Bonneville International. He was chairman of the Scripture Publication Committee in the 1970s that oversaw publication of the LDS Church edition of the King James Bible, and revised editions of church scriptures containing footnotes and guides. He also oversaw the church's Printing Advisory, Missionary Executive, and General Welfare committees. While an apostle, he continued his education and received a master of Business administration degree from Brigham Young University in 1974.

Monson received the Boy Scouts of America's Silver Beaver award in 1971 and Silver Buffalo award in 1978, the latter being the highest honor of the BSA. In October 1993, during the Priesthood Session of the church's general conference, Monson also received the Bronze Wolf, the highest honor and only award of the World Organization of the Scout Movement, and was recognized for his contributions when a leadership complex at the Summit Bechtel Reserve was named for him. The citation for this award says,

Monson later oversaw church operations in Eastern Europe and helped the church gain access in the Soviet bloc. On 29 August 1982, he organized the first stake in East Germany and was instrumental in obtaining permission for the LDS Church to build a temple in Freiberg, East Germany, which was completed in 1985.

As a counselor in the First Presidency, Monson dedicated seven church temples: Buenos Aires Argentina, 1986; Louisville Kentucky, 2000; Reno Nevada, 2000; Tampico México, 2000; Villahermosa México, 2000; Mérida México, 2000; and Veracruz México, 2000. Monson attended the dedication of many other LDS Church temples as a member of the Quorum of the Twelve and the First Presidency.

Monson was ordained an LDS apostle at age 36, served in the First Presidency under three church Presidents and was the President of the Quorum of the Twelve Apostles from March 12, 1995, until he became President of the Church on February 3, 2008. He succeeded Gordon B. Hinckley as church President.

Monson resigned most of his positions in 1996 when church leadership determined all the general authorities should leave all Business boards of Directors, except for Deseret Management Corporation. From 1965 until 1996 Monson was a member of the Deseret News Publishing Company board of Directors. He became chairman of the board of Directors in 1977.

In June 2008, Monson and his counselors in the First Presidency sent a letter to local congregations in California, urging them to support Proposition 8 by donating their time and resources, stating that, "Our best efforts are required to preserve the sacred institution of marriage." In the 2012 Utah voter list he was listed as a registered Republican voter.

In Slate.com's "80 Over 80," a list of the most powerful octogenarians, Monson placed first in 2009, and first again in 2010. In 2011, Gallup listed Monson as one of "Americans' 10 Most Admired Men".

In connection with the LDS Church's centennial celebration as a chartered sponsor, the BSA announced that the Leadership Excellence Complex, located at The Summit Bechtel Family National Scout Reserve in West Virginia, would be renamed the Thomas S. Monson Leadership Excellence Complex and also awarded him Scouting's Honor Medal in 2013 for saving the life of a girl who was drowning when he was 12 years old. The Salt Lake chapter of Rotary International honored Monson at its international convention with its Worldwide Humanitarian Award in 2008.

After college he rejoined the Naval Reserve with the aim of becoming an officer. Shortly after receiving his commission acceptance letter, his local bishop asked him to serve as a counselor in the bishopric. Time conflicts with bishopric meetings would have made Navy Service impossible. After discussion with church apostle Harold B. Lee (his former stake president), Monson declined the commission and applied for a discharge. The Navy granted his discharge in the last group processed before the Korean War. Lee set him apart six months later as a bishop—mentioning in the blessing that he likely would not have been called if he had accepted the commission.

On May 23, 2017, the LDS Church said Monson would no longer be attending meetings at the church's offices on a regular basis, because of limitations incident to age. With his birthday on August 21, 2017, Monson became the seventh President of the LDS Church to be a nonagenarian. Consistent with the May 2017 statement, the LDS Church announced on September 28, 2017, that Monson would not attend the church's upcoming general conference, due to age-related limitations.

Monson died of natural causes at the age of 90 on January 2, 2018, at his home in Salt Lake City. The following day, the LDS Church announced that a public viewing would be held on January 11, in the church's Conference Center, with funeral services scheduled the following day, also in the Conference Center. He was succeeded as church President by Russell M. Nelson.