Laurel Amy Eva Doyle was born on 15 March 1902 in Doyleston, the Canterbury town named after her grandfather, Joseph Hastings Doyle. She was the eldest of two daughters and two sons of William John Doyle, a storekeeper, and his wife, Matilda Jane McCausland. Her father, like his father before him, was a noted judge of horseflesh. When Laurel's mother died in 1909, William Doyle became a full-time horse breeder, trainer and dealer, with a particular interest in racehorses. In 1917 he married Elsie Agnes Hibberd, and this union produced another family of two boys and two girls.
Laurel Doyle was an accomplished rider from an early age. She continued to compete in the show ring as an adult, winning the 'best lady rider' title at the annual Christchurch show for several years. She worked in her father's racing stables and trained her first thoroughbred winner at the age of 20. As owner of the horse she needed no official permission for this, but in order to train for others she required a licence from the New Zealand Racing Conference. This was granted in February 1927, making her the second woman (after Granny Maher in 1924) to become a professional racehorse trainer in New Zealand.
Laurel Doyle began her career as private trainer for Alec Roberts, a notable figure in racing history. He was the owner of Seadown Stud, Timaru, and breeder of the legendary Phar Lap. Ironically, Phar Lap was sent to the 1928 national yearling sales while the two 'best' yearlings from the crop were kept back to be raced by their owner. One of them won several minor events under Laurel's care.
On 30 May 1929 at Christchurch, Laurel quietly married James Campbell, a Scottish-born jockey. Their daughter was born five months later. The union dismayed both her family and the Canterbury racing community. The Doyles were well respected, and Laurel was admired for her attractive appearance and fastidiousness of dress and habits. Jim Campbell, although a talented rider and with personal charm, had a severe drinking problem. His behaviour had brought many official warnings and disqualifications, and at the time of their marriage his jockey's licence had been cancelled.
The marriage faced further difficulties. Laurel continued to train for many prominent owners, including her brother Bill, after Roberts gave up his racing interests. She was regarded as head of the household and the breadwinner. They moved to a spacious house near the Riccarton racecourse, which was almost certainly financed by Laurel and her family.
Bill Doyle's horse, Thurina, gave Laurel Campbell her first major race victory by winning the New Zealand Grand National Steeplechase at Riccarton in 1933. That season, 'Mrs J. Campbell', as she was listed, came seventh on the trainers' table with 22 winners, exactly equal with Granny McDonald (formerly Maher) and ahead of the vast majority of male trainers. Laurel trained Vintage to win the 1935 Wellington Cup, while Willie Win ran second in the 1937 Melbourne Cup after some major victories in New Zealand.
By this time she had endured the tragedy of her daughter's death. Aged six, 'wee Janny' had been hit by a truck outside her home on 16 December 1935 and died hours later. The marriage foundered as Jim Campbell sank further into alcoholism and Laurel devoted herself to her horses.
Eventually, about 1943, she sold the house and moved to Hastings, where she went into partnership with Jack Jefferd, an English-born trainer. Together they achieved what neither had done separately: headed the trainers' table, in the 1947–48 season. They also established a personal liaison which caused great distress to Jefferd's wife and family. The partnership gave Campbell her second Grand National Steeplechase when Bandmaster won in 1951, but soon afterwards she returned permanently to Christchurch.
Laurel Campbell and her husband were divorced in 1950. Jim died in 1956 in Porirua Hospital, a mental asylum, and Laurel on 3 January 1971, in a similar establishment, Sunnyside Hospital, Christchurch. She died of a heart attack, having suffered severe depression for six years.