The younger Exner was interested in drawing and painting from an early age and was put in private training after his confirmation.
He began to study at the Royal Danish Academy of Art (Det Kongelige Danske Kunstakademi) April 1839, where he intended on becoming a history painter.
In 1849 one of his history paintings, "Thyra Danebod forsøger at formilde Gorm den Gamles vrede mod nogle fangne kristne" ("Thyra Danebod Tries to Placate Gorm the Elder's Anger with Imprisoned Christians"), was purchased by the Danish Royal Painting Collection, now the Danish National Gallery (Statens Museum for Kunst).
But even Exner admitted to having an irrational "emotional desire to become a history painter" ("usalige lyst til at blive historiemaler").
This brought him to Amager, an island south of Copenhagen, where Dutch farmers had settled in 1521, but who were still relatively unknown to their fellow Danes.
There he painted his masterly, life-size "En Amagerkone, der tæller sine Penge efter" ("A Woman from Amager Counting Her Money"), which was exhibited in 1852, and was purchased by the National Collection.
They had been affected by Eckersberg's stress on attentive study and representation of Danish nature, as well as by the technical skills he taught them to achieve those goals.
He often traveled to the countryside during the summers to do live studies from nature, as was common practice in these times, working up finished paintings in the studio during the winter.
And he also began seeking out themes in other locations on Sjælland.as well, which resulted in "Et Bondegilde i Hedeboegnen" ("A Party on the Farm in the Hedebo Area") painted in 1856, as well as others of the same ilk.
One of his paintings "Lille pige lader en gammel mand lugte til en blomst" ("A Little Girl Lets an Old Man Smell a Flower") painted in 1856, proved to be the start of Heinrich Hirschsprung's collection (the museum now known as the Hirschsprung Collection in Copenhagen), when he purchased it in 1866.
In an age where industrialisation was fast encroaching on traditional farmlife, Exner depicted a timeless vision of several generations of farm folk, gathered around in their idealised and cheerful house, self-sufficient and happy.
There he found a group of people whose lives interested him deeply, a folk who were fast becoming extinguished in the social changes of that time.
Exner was a master of composition setting up a lively combination of characters, costumes, and interiors, along with an underlying anecdote, that showed an inspiration of Dutch and German paintings.