Robert Edwin Peary was born on May 6, 1856, in Cresson, Pennsylvania, to Charles N. and Mary P. Peary. After his father died in 1859, Peary's mother took the boy with her and settled in Portland, Maine. After growing up in Portland, Peary attended Bowdoin College, some 36 miles (58 km) to the north. He was a member of the Delta Kappa Epsilon and Phi Beta Kappa fraternities while at college. He graduated in 1877 with a civil engineering degree.

Peary resided in Fryeburg, Maine, in 1878–1879. During that time he made a profile survey from the top of Fryeburg's Jockey Cap Rock. The 360 degree survey names the larger hills and mountains visible from the summit. His boyhood friend, Alfred E. Burton, suggested that the profile survey be made into a monument. The survey was cast in bronze and set atop a granite cylinder, and erected to his memory by the Peary Family in 1938. A hike of less than a mile leads visitors to the summit and the monument.

After college, Peary worked as a draftsman making technical drawings in Washington, DC, at the US Coast and Geodetic Survey office. He joined the United States Navy and on October 26, 1881, was commissioned as a civil Engineer, with the relative rank of lieutenant. From 1884 to 1885 he was assistant Engineer on the surveys for the Nicaragua Canal, and later became the Engineer in charge. As reflected in a diary entry he made in 1885, during his time in the Navy, he resolved to be the first man to reach the North Pole.

Peary made his first expedition to the Arctic in 1886, intending to cross Greenland by dog sled, taking the first of his own suggested paths. He was given six months' leave from the Navy, and he received $500 from his mother to book passage north and buy supplies. He sailed on a whaler to Greenland, arriving in Godhavn on June 6, 1886. Peary wanted to make a solo trek but a young Danish official named Christian Maigaard convinced him he would die if he went out alone. Maigaard and Peary set off together and traveled nearly 100 miles (160 km) due east before turning back because they were short on food. This was the second-farthest penetration of Greenland's ice sheet at that date. Peary returned home knowing more of what was required for long-distance ice trekking.

Back in Washington attending with the US Navy, Peary was ordered in November 1887 to survey likely routes for a proposed Nicaragua Canal. To complete his tropical outfit he needed a sun hat, so he went to a men's clothing store. There he met 21-year-old Matthew Henson, a black man working as a sales clerk. Learning that Henson had six years of seagoing experience as a cabin boy, Peary immediately hired him as a personal valet.

On August 11, 1888, Peary married Josephine Diebitsch, a Business school valedictorian who thought the modern woman should be more than just a mother. Diebitsch had started working at the Smithsonian Institution when she was 19–20 years old, replacing her father after he became ill and filling his position as Linguist. She resigned from the Smithsonian in 1886 upon becoming engaged to Peary.

Peary was unable to fully enjoy the fruits of his labors. Upon returning to civilization, he learned that Dr. Frederick A. Cook, who had been a surgeon on the 1891–1892 Peary expedition, claimed to have reached the pole in 1908. After some court trials, Peary was proved right, and Cook was declared wrong.

Peary's leg mended in February 1892. By April, he made some short trips with Josephine and an Inuit dog sled driver to native villages to purchase supplies. On May 3, 1892, Peary finally set out on the intended trek with Henson, Gibson, Cook and Astrup. At about the 150-mile (240 km) mark, Peary continued on with Astrup. The two found the 1,000-metre (3,300 ft) high view from Navy Cliff to be revealing: they saw Independence Fjord and concluded that Greenland was an island. The men trekked back to Red Cliff and got there on August 6, having traveled a total of 1,250 miles (2,010 km).

As a result of Peary's 1898–1902 expedition, he claimed an 1899 visual discovery of "Jesup Land" west of Ellesmere. He claimed that this sighting of Axel Heiberg Island was prior to its discovery by Norwegian Explorer Otto Sverdrup's expedition. This contention has been universally rejected by exploration societies and historians. However, the American Geographical Society and Royal Geographical Society of London honored Peary for tenacity, mapping of previously uncharted areas, and his discovery in 1900 of Cape Jesup at the north tip of Greenland. Peary also achieved a "farthest north" for the western hemisphere in 1902 north of Canada's Ellesmere Island.

In April 1886 he wrote a paper for the National Academy of Sciences proposing two methods for crossing Greenland's ice cap. One was to start from the west coast and trek about 400 miles (640 km) to the east coast. The second, more difficult path was to start from Whale Sound at the top of the known portion of Baffin Bay and travel north to determine whether Greenland was an island or if it extended all the way across the Arctic (1,300 miles). Peary was promoted to the rank of lieutenant commander on January 5, 1901, and to commander on April 6, 1902.

After returning to Roosevelt in May, Peary in June began weeks of difficult travel by heading west along the shore of Ellesmere. He discovered Cape Colgate, from the summit of which he claimed in his 1907 book that he had seen a previously undiscovered far-north "Crocker Land" to the North West on June 24, 1906. A later review of his diary for this time and place found that he had written, "No land visible." On December 15, 1906, the National Geographic Society of the United States, which was primarily known for publishing a popular magazine, certified Peary's 1905-6 expedition and "Farthest" with its highest honor, the Hubbard Gold Medal. No major professional geographical society followed suit. In 1914 Donald MacMillan and Fitzhugh Green's expedition found that Crocker Land did not exist.

For his final assault on the Pole, Peary and 23 men, including Ross Gilmore Marvin, set off from New York City on July 6, 1908 aboard the SS Roosevelt under the command of Captain Robert Bartlett. They wintered near Cape Sheridan on Ellesmere Island, and from Ellesmere departed for the pole on February 28 – March 1, 1909. The last support party was turned back from "Bartlett Camp" on April 1, 1909, in latitude no greater than 87°45' north. (The figure commonly given, 87°47', is based upon Bartlett's slight miscomputation of the distance of a single Sumner line from the pole.) On the final stage of the journey toward the North Pole, Peary told Bartlett to stay behind. He continued with five assistants, none capable of making navigation observations: American Matthew Henson, and Inuit Ootah, Egigingwah, Seegloo and Ooqueah. On April 6, 1909, he established "Camp Jesup" allegedly within 5 miles (8.0 km) of the pole.

Supporters of Peary and Henson assert that the depth soundings they made on the outward journey have been matched by recent surveys, and so their claim of having reached the Pole is confirmed. Only the first few of the Peary party's soundings, taken nearest the shore, touched bottom; experts have said their usefulness is limited to showing that he was above deep water. Peary stated (in 1909 Congressional hearings about the expedition) that he made no longitudinal observations during his trip, only latitude observations, yet he maintained he stayed on the "Columbia meridian" all along, and that his soundings were made on this meridian. The pack ice was moving all the time, so he had no way of knowing where he was without longitudinal observations.

The National Geographic Society limited access to Peary's records. At the time, his proofs were not made available to scrutiny by other professionals, as had been done by the Danish panel. Gilbert Grosvenor persuaded the National Academy of Sciences not to get involved. The Royal Geographical Society (RGS) of London gave Peary its gold medal in 1910, despite internal council splits which only became known in the 1970s. The RGS based their decision on the belief that the NGS had performed a serious scrutiny of the "proofs", which was not the case. Neither the American Geographical Society nor any of the geographical societies of semi-Arctic Scandinavia has recognized Peary's North Pole claim.

The conflicting and unverified claims of Cook and Peary prompted Roald Amundsen to take extensive precautions in navigation during his Antarctic expedition so as to leave no room for doubt concerning his 1911 attainment of the South Pole, which (like Robert Scott's a month later in 1912) was supported by the sextant, theodolite, and compass observations of several other navigators. See Polheim.

In early 1916, Peary became chairman of the National Aerial Coast Patrol Commission, a private organization created by the Aero Club of America. It advocated the use of aircraft in detecting warships and submarines off the U.S. coast. Peary used his Celebrity to promote the use of military and naval aviation, which led directly to the formation of Naval Reserve aerial coastal patrol units during the First World War.

Admiral Peary died in Washington, D.C. on February 20, 1920. He was buried in Arlington National Cemetery. More than 60 years later, Matthew Henson was honored by being re-interred nearby in Arlington Cemetery on April 6, 1988.

E.L. Doctorow's novel Ragtime (1974) has as a major character Father, a member of Peary's 1908 polar expedition. The expedition is described from the point of view of one not chosen for the final polar attempt.

While in the Arctic years later, Peary had a long-term relationship with an Inuit woman, Aleqasina (who is estimated to have been 14 when they began). She bore him at least two children, including a son Kali, identified in the late 1980s when he was an octogenarian.

In 1984 the National Geographic Society (a major sponsor of Peary's expeditions) commissioned the Arctic Explorer Wally Herbert to write an assessment of Peary’s original 1909 diary and astronomical observations. As Herbert researched the material, he came to believe that Peary must have falsified his records and concluded that he did not reach the Pole. His book, The Noose of Laurels, caused a furor when it was published in 1989. His conclusion has been widely accepted. Herbert, who reached the Pole in 1969, is recognized as the first man leading a team to reach the Pole.

S. Allen Counter, a Harvard neuroscience professor, was interested in learning more about Henson's role in the Arctic expeditions. In 1986 he went to Greenland to do research and found Peary's son Kali and Henson's son Anaukaq, then octogenarians, and some of their descendants. He arranged to bring the men and their families to the United States to meet their American relatives and see their fathers' gravesites. Counter wrote about Peary's and Henson's Inuit children, and their meeting with their American half-siblings and other relatives in his book, North Pole Legacy: Black, White and Eskimo (1991). He also gained national recognition of Henson's role in the expeditions. A subsequent documentary by the same name was also released.

Pierre Berton Canadian author and Historian, wrote extensively about Peary and his Arctic expeditions in his book: (1988 Anchor Canada ISBN 0-385-65845-1. OCLC 46661513.) The Arctic Grail: The Quest for the North West Passage and the North Pole, 1818–1909.

The NGS commissioned the Foundation for the Promotion of the Art of Navigation to resolve the issue. Reporting on its conclusion that Peary had reached the Pole, Gilbert M. Grosvenor, President of the NGS, said, “I consider this the end of a historic controversy and the confirmation of due justice to a great Explorer.” The Navigation Foundation's full report of December 11, 1989 has been published and is available here.

Peary's exploits and life were portrayed in the 1998 TV movie Glory & Honor. Henry Czerny played Robert Peary. His associate Matthew Henson was played by Delroy Lindo. The film won a Primetime Emmy and Lindo won a Golden Satellite Award for his performance.

The Explorer Major General Adolphus Greely noted that no Arctic expert questions that Peary courageously risked his life traveling hundreds of miles from land, and that he reached regions adjacent to the pole. (After initial acceptance of Peary's claim, he later came to doubt Peary's having reached 90°.) In his book Ninety Degrees North: The Quest for the North Pole (2001), polar Historian Fergus Fleming describes Peary as "undoubtedly the most driven, possibly the most successful and probably the most unpleasant man in the annals of polar exploration."

British Explorer Tom Avery and four companions recreated the outward portion of Peary's journey in 2005, using replica wooden sleds and Canadian Eskimo Dog teams. They ensured their sled weights were the same as Peary's sleds throughout their journey. They reached the North Pole in 36 days, 22 hours – nearly five hours faster than Peary. Avery writes on his web site that

The last five marches when Peary was accompanied by a navigator (Capt. Bob Bartlett) averaged no better than 13 miles (21 km) march northing. But once the last support party turned back at "Camp Bartlett" from where Bartlett was ordered southward, at least 133 nautical miles (246 km) from the pole, Peary's claimed speeds immediately doubled for the five marches to Camp Jesup, and then quadrupled during the 2½ day return to Camp Bartlett—at which point his speed slowed drastically compared to that pace. Peary's account of a beeline journey to the pole and back — which would have assisted his claim of such speed — is contradicted by companion Henson's account of tortured detours to avoid "pressure ridges" (ice floes' rough edges, often a few meters high) and "leads" (of open water between those floes).