Abrahams’s father, Isaac, was a Jewish immigrant from Congress Poland. He worked as a financier, and settled in Bedford with his Welsh Jewish wife, Ester. Harold was born in Bedford, and was the younger brother of another British athlete, the Olympic long jumper Sir Sidney Abrahams. Another brother, Sir Adolphe Abrahams, became the founder of British sport medicine.

Before attending university, Abrahams served as a lieutenant in the British Army. He attended Bedford School, Repton School and then at Gonville and Caius College, Cambridge, from 1920 to 1924. He afterwards trained as a lawyer. At Cambridge, he was a member of the Cambridge University Athletics Club (of which he was president 1922–1923), Cambridge University Liberal Club, the Pitt Club, and the Gilbert and Sullivan Society.  Abrahams was also a member of the Achilles Club, a track and field club formed in 1920 by and for past and present representatives of Oxford and Cambridge universities. One of the club’s founding members was Aubrey Montague, who like Abrahams is also immortalized in the 1981 film Chariots of Fire.  A sprinter and long jumper since his youth, he continued to compete in sport while at Cambridge. He earned a place in the 1920 Olympic team, but was eliminated in the quarter-finals of both the 100 m and 200 m, and finished 20th in the long jump. He was also part of the British relay team that took fourth place in the 4 x 100 m.

Although Abrahams dominated British long jump and sprint events, after graduating from Cambridge he employed Sam Mussabini, a professional coach, who improved his style and training techniques in preparation for the 1924 Olympics in Paris, France.  For six months, Mussabini at Abrahams’s direction emphasized the 100 m, with the 200 m as secondary. Through vigorous training, Abrahams perfected his start, stride, and form. One month before the 1924 Games, he set the English record in the long jump 24 feet 2 1⁄2 inches (7.38 m), a record which stood for the next 32 years. The same day he ran the 100 yard dash in 9.6 seconds, but the time was not submitted as a record because the track was on a slight downhill.

At the 1924 Summer Games, Abrahams won the 100 m in a time of 10.6 seconds, beating all the American favourites, including the 1920 gold-medal winner Charley Paddock. In third place was Arthur Porritt, later Governor-General of New Zealand and Queen’s Surgeon. The Paris Olympics 100 m dash took place at 7 p.m. on 7 July 1924, and Abrahams and Porritt dined together at 7 p.m. on 7 July every year thereafter, until Abrahams’s death in 1978. Teammate Eric Liddell, the British 100 yard dash record holder at that time, declined to compete in the Paris 100 m as one of the heats for the event was held on a Sunday. Both Liddell and Abrahams competed in the final of the 200 m race, however, with Liddell finishing third and Abrahams sixth. As an opening runner for the 4 x 100 m team, Abrahams won a second Olympic medal, a silver. He did not compete in the long jump.

In May 1925, Abrahams broke his leg while long-jumping, ending his athletic career. He returned to his legal career. In 1928, he was team captain of the British Olympic team at Amsterdam and editor of the Official British Olympic Report for the same games. Subsequently he worked as an athletics journalist for forty years, becoming a commentator on the sports for BBC radio. In 1936, he reported the Berlin Olympics for the BBC. Later in his life, he also became president of the Jewish Athletic Association, and served as chairman for the Amateur Athletic Association (AAA).  Abrahams wrote a number of books, including The Olympic Games, 1896-1952 and The Rome Olympiad, 1960. Although not an official timer, Abrahams was present when Roger Bannister broke the four-minute mile in 1954.  Abrahams died in Enfield on 14 January 1978, aged 78. He was buried in the same grave as his wife Sybil Evers, in Saint John the Baptist Churchyard in Great Amwell, Hertfordshire.

While at Cambridge, Abrahams was romantically involved with the seriously academic Christina McLeod Innes, and they became informally engaged, but their relationship waned and ended as Abrahams began focusing exclusively on his athletics and the Olympics. In early 1934, he met D’Oyly Carte Opera Company singer Sybil Evers, and they began a passionate on-and-off romance.  According to his biographer Mark Ryan, Abrahams had a fear of commitment and old-fashioned ideas about the role of women in marriage, but he was able to overcome these, and the couple wed in December 1936. In the film Chariots of Fire, Evers is misidentified as D’Oyly Carte soprano Sybil Gordon (portrayed by Alice Krige), and the film portrays the couple as meeting a decade earlier than they actually did.

Sybil Evers could not have children, so they adopted an eight-week-old boy, Alan, in 1942, and a nearly three-year-old girl, Sue, in 1946; Sue later married nuclear activist Pat Pottle. During the Nazi regime and war, the couple also fostered two Jewish refugees: a German boy called “Ken Gardner” (born Kurt Katzenstein), and an Austrian girl named Minka.  Evers died in 1963 at the age of 59, and Harold set up two awards in her name: the Sybil Evers Memorial Prize for Singing (1965–1995), an annual cash prize awarded to the best female singer in her last year at the Webber Douglas School of Singing and Dramatic Art, and the Sybil Abrahams Memorial Trophy, presented each year from 1964 onward at Buckingham Palace by the Duke of Edinburgh, President of the British Amateur Athletics Association, to the best British woman athlete.

Abrahams was appointed a Commander of the Order of the British Empire (CBE) in 1957. Abrahams has been recognized with an English Heritage Blue plaque at his former home in Golders Green in northwest London, which was unveiled by his daughter Sue Pottle (wife of Pat Pottle) and nephew Tony Abrahams. Abrahams lived at Hodford Lodge, 2 Hodford Road, from 1923 to 1930, years during which he achieved his greatest successes.

A plaque from the Heritage Foundation was unveiled at his birthplace, Rutland Road in Bedford, on July 8, 2012. This coincided with the Olympic torch relay passing through the town.  Abrahams was immortalised in the 1981 film Chariots of Fire, in which he was played by British actor Ben Cross. The film won four Academy Awards, including Best Picture. His memorial service serves as the framing device for the movie, which tells his story and that of Liddell.  Abrahams was inducted into the International Jewish Sports Hall of Fame in 1981 and into the England Athletics Hall of Fame in 2009.

In July 2012 plans were announced to erect a memorial to Abrahams in Telford, Shropshire to recognise that before the 1924 Olympics he won a gold medal in the 100 yard sprint at the Midlands Area AAA championships at St George’s Recreation Ground.  Norris McWhirter once commented that Abrahams “managed by sheer force of personality and with very few allies to raise athletics from a minor to a major national sport”. Reflecting in 1948 on Abrahams’ athleticism, Philip Noel-Baker, Britain’s 1912 Olympic captain and a Nobel Prize winner, wrote:

I have always believed that Harold Abrahams was the only European sprinter who could have run with Jesse Owens, Joe Candito, Ralph Metcalfe, and the other great sprinters from the U.S. He was in their class, not only because of natural gifts — his magnificent physique, his splendid racing temperament, his flair for the big occasion — but because he understood athletics and had given more brainpower and more will power to the subject than any other runner of his day.