According to Wahlberg's own statement, the father was a professional painter, the mother is said to have been the daughter of an Italian sculptor. The young Wahlberg learned his father's trade, but showing early musical aptitude, he became a student at the Royal Academy of Music, where he studied piano and clarinet playing. For some time he was employed in Göta garde's music band. His youth was industrious and anxious; he barely made a living with piano lessons, drew for a few years in the Art Academy's principle school, but never became a student at the academy, however decided on the path of an artist, painted small landscapes and in 1856 had to sell a small painting to the Art Association for the first time. In 1857 he settled in Düsseldorf. There he was a student of Hans Fredrik Gude for a short time, but mostly painted on his own, had to sell paintings in Germany and to the Art Association at home, made a study trip to Holland and Belgium, then returned to Stockholm in 1862 and remained resident there for the next four years . ​ Among his paintings done in Düsseldorf are Sunset in Bohuslän, a couple of Swedish forest landscapes and Winter landscape with bear hunting (1861, the figures, the bear and the dogs painted by Josef Wilhelm Wallander, Härnösand museum).

 

During the Stockholm period, Storm on the Dutch coast (1863) and Fors in the Swedish countryside (the latter two strongly influenced by Andreas Achenbach), Burgruinen Niedeck by the Rhine (1863, Uppsala museum), Forest party from Särö (1865, Gothenburg art museum) were added, among others. Hörningsholm in the moonlight (1866) and Swedish lake landscape from Kolmården (same year, National Museum). The latter painting – a carefully composed expansive view of rugged woodland, lake and summer sky – became highly acclaimed and marks the pinnacle of the artist's development up to that point. ​ In a smaller Kolmård motif (1865; Örebro County Museum), Wahlberg depicted a summer evening with moonlight, kept bright in soft, melting colors. He was still bound by the limitation of his technique, but the latter painting pointed forward.

 

The big cover followed, since Wahlberg settled in Paris in 1866. The two works he exhibited at the Salon in 1868 – a moonlight and a sunset mood at a fishing village in Bohuslän (National Museum) – mark his transition from Düsseldorf technique to modern French treatment. He easily acquired the study method and technique of the French school, was successful, won medals at the Salons of 1870 and 1872 and became the introducer of modern landscape art into Swedish painting. His landscapes from this time are large and fully seen. They are magnificent studio works, painted with breadth and boldness and at the same time with refined elegance. Alongside his golden evening moods and his lyrical moonlight stand his depictions of the Swedish countryside with meadows, forests and lakes in full midday sun.

 

​The main numbers in his creations during these years include Utsikt i Södermanland (over meadow and lake, 1870), Landscape in moonlight (same year), Moonlight from southern France (same year, both in the National Museum), Nääs (summer evening, 1871, Stockholm Palace ), In Vaxholm (an autumn day, 1872, National Museum), In Fontainebleauskogen (1874, powerful and large held), May in Nizza (1878), Evening on Halland's Väderö (1800), Fjällbacka (moonlight, 1881), Swedish birch grove (1882 , the last four in Gothenburg's art museum). At the 1878 World's Fair, Wahlberg had been awarded a first-class medal. He became a member of the Swedish Academy of Arts in 1866, and in 1880 he became a non-tenured deputy professor. Almost every summer he stayed in Sweden, in different regions, in Stockholm's archipelago, on the west coast, in Scania, Halland, Värmland. ​ Among his works from the latter part of the 1880s onwards, Stockholm's current, night time and the same motif in winter mist (both 1888), Moonlight on Halland's Väderö (1889, Copenhagen Art Museum), October Night and the broadly and summarily painted night mood Poplar (1893 ).

 

Towards the end of the century, Wahlberg's search became more restless and experimental. He settled on a strong and variegated color scale and on a treatment in dotted patterns. A simple and convincing mood could still be evoked in some of his last works, for example Sun on Snow in Marstrand and Swedish Summer Night (both 1901). In his less elaborate studies, the painter's lively feeling for nature found fresh, intimate, immediate expression. Wahlberg was a newsman in Swedish painting, but not in French, where he joined an already developed and recognized direction. He initially caused dissatisfaction among the representatives of the düsseldorf landscape in Sweden, an irritation which, however, did not last long. ​

 

At the National Museum, Wahlberg is represented, in addition to the above-mentioned paintings, by several studies (especially notable is the large study Mountain and Clouds, which shows a powerful and powerful spread) and also by a number of drawings from his various stages. From his last time, the museum owns the Moonshine, motif from Ronneby (1900). Gothenburg's museum owns about ten canvases.