This breed has a thick and dense double coat[citation needed]; the Leonberger is a large, muscular, and elegant dog with balanced body type, medium temperament, and dramatic presence.

A sexually dimorphic breed, the Leonberger possesses either a strongly masculine or elegantly feminine form, making gender immediately discernible.

Seen in profile, the chest curves inward from the prosternum, tangentially joins at the elbow to its underline at 50% of the withers' height, and then continues slightly upward toward the stifle.

[4] Both a necessity for work and a defining attribute of the breed, the Leonberger has a dense water-resistant long double coat on the body that is complemented by the shorter, fine hair on the muzzle and limbs.

Robust, loyal, intelligent, playful, and kindly, they can thus be taken anywhere without difficulty and adjust easily to a variety of circumstances, including the introduction of other dogs.

[3] A 2024 UK study found a life expectancy of 10 years for the breed compared to an average of 12.7 for purebreeds and 12 for crossbreeds.

[12] A study found a high prevalence of neurological conditions in the Leonberger, which is likely due in large part to limited genetic diversity.

[15] Another disease described in the breed is the juvenile-onset leukoencephalomyelopathy caused by an autosomal recessive variant in the NAPEPLD gene.

[10] A study in the UK of more than 900,000 dogs looking at the annual prevalence of osteosarcoma found the Leonberger to have the second highest rate, at 1.48%, compared to 0.037% overall.

[17] In the 1830s, Heinrich Essig, a dog breeder and seller and mayor of the town of Leonberg near Stuttgart in Baden-Württemberg, Germany, claimed to have created the Leonberger by crossing a female Landseer Newfoundland with a "barry" male from the Great St Bernard Hospice and Monastery (which would later create the Saint Bernard).

[21] At the time, Essig's Leonbergers were denounced as an indifferent knockoff of a St. Bernard—not a stable and recognized breed—and a product of a popular fad or fashion for large and strong dogs, fomented in part by Essig's prodigious marketing skills (he gave dogs to the rich and famous).

[1][21] The modern look of the Leonberger, with darker coats and black masks, was developed during the latter part of the 20th century by reintroducing other breeds, such as the Newfoundland.

[32] The Leonberger received American Kennel Club recognition as a member of the Working Group[1][33] on January 1, 2010, alongside the Icelandic Sheepdog and the Cane Corso.

[36] The graphic music video "Deutschland" by German rock band Rammstein portrays the symbolic figure of Germania giving birth to Leonberger puppies.

[38] In Norwegian author Karin Fossum's Inspector Sejer series, the title character has a Leonberger named Kollberg.

[39] Three Leonberger dogs[40][41] (one was a female, and two males)[citation needed] played the main character Buck in The Call of the Wild: Dog of the Yukon (1997), a Canadian rendition of Jack London's Call of the Wild which stars Rutger Hauer as John Thornton and is narrated by Richard Dreyfuss.