Two of his children, Louis and Pauline, are 11th and 12th in the line of succession to the Monegasque throne.
Ducruet was born in Beausoleil, Alpes-Maritimes to Henri Ducruet, a manual laborer and his wife Maguy (née Barbero), a homemaker.
Ducruet attended the University of Nice but dropped out after a year. He worked as a bodybuilder, pet shop clerk and a fishmonger before being accepted into Monaco's police force as a trainee officer in 1986.
Within two years he had been appointed a Palace bodyguard with responsibility for Prince Albert. In 1991, he was appointed by Prince Rainier to accompany his daughter Princess Stéphanie as bodyguard on her ill-fated tour to promote her record album.
Daniel has since launched a career as a singer releasing two albums Pourquoi Pas and Jamais personne, with little success. He also wrote a book about his life with the Grimaldi family.
In 2004 he has taken part in the Italian reality TV show La Fattoria and the similar French reality TV show La Ferme Célébrités, where he finished second. Also in 2004 he hosted Real TV, the Italian version of Real TV, on Italia 1.
Ducruet's first marriage to Sandra Naccache ended in divorce in the mid-1980s.
Ducruet's girlfriend Martine Malbouvier was six months pregnant with his first child, when he went public with his relationship with Princess Stéphanie. His first son, Michaël Ducruet, was born in February 1992. On 26 November 1992, ten months after the birth of his first child, Ducruet had a second son Louis Robert Paul with Princess Stéphanie.
Stéphanie campaigned long and hard for her father to approve a marriage between her and Ducruet, since he was reluctant to sanction a marriage between the two. Only after the birth of their second child, a daughter Pauline Grace Maguy Ducruet, born on 4 May 1994, and his own double-bypass surgery did Prince Rainier give his blessing. Louis and Pauline Ducruet were legitimated by their parents' marriage and are currently 11th and 12th in the line of succession to the Monégasque throne.
On 1 July 1995 Ducruet and Princess Stéphanie were married in a civil ceremony at the Monaco's Palace Princier.
Ducruet and Princess Stéphanie jointly invested in the Replay Store and Replay Cafe in Monaco.
In September 1996, Ducruet's infidelity with Muriel "Fili" Mol-Houteman, Miss Bare Breasts of Belgium 1995 was photographed by the paparazzi and the images were published in the Italian tabloids Evatremila and Gente. Ducruet claimed that he was set up. At the height of the scandal, a 90-minute video of the Ducruet's encounter with Houteman sold in Italy. When the story made headlines, Ducruet fled to Morocco. Upon his return he met with his wife who submitted a written request for a divorce from her father on 16 September 1996. Princess Stéphanie divorced Ducruet on 4 October 1996.
After the divorce, Stéphanie bought his share of their joint business interest in Replay Restaurant on Rue Grimaldi.
After the publication of the compromising photographs and video footage of Ducruet and Muriel "Fili" Mol-Houteman, Ducruet took legal action.
He claimed that Mol-Houteman had conspired with photographer Stephane de Lisiecki and his assistant Yves Hoogewys to breach his privacy for financial gain. He also claimed that Mol-Houteman drugged his champagne.
Mol-Houteman received a six-month suspended sentence, while Lisiecki and Hoogewys were given one-year suspended sentences. Ducruet was awarded $27,930 in damages by the court for breaches of privacy.