While he was studying, he got his first poem published in Upsala tidningar (1802). The following years he wrote and translated several other poetic works, and received several awards from the Swedish Academy for his work. Among his awarded works were translatations of Horace and Virgil; and for a song about Gustav III he was awarded the high sum of 200 ducats. His poetry was, however, by some considered too rhetorical and out-dated compared to the then flourishing Romantic poets. Wallin did not take the criticism light-hearted, but adapted to the new style which was more emotional and less influenced by the Latin poets.
He held many different clerical posts throughout his life. Ultimately he was ordained Archbishop of Sweden in 1837. But before he even had moved to Uppsala (seat of the bishoprick), he died a sudden death in 1839, and was buried in Stockholm. The Swedish Biographical Dictionary of 1906 indicates that he at his death was "mourned by the entire Swedish people". The Swedish Literature in Summary (1904) writes that no Swedish orator or preacher ever had his distinctive glow as a speaker.
He was undoubtedly a talented person in literature and a most pious man. But he was weak in body, and this trait in combination with his strong work ethic may have caused stress on his health.
Besides hymns, Wallin wrote several secular poems highly praised in his time. He published several sermons and speeches. Of his hymns still in use in Swedish hymnbooks today, a few have also been translated into English and published in hymnals such as the Lutheran Book of Worship. These include——besides "Var hälsad sköna morgonstund" ("All Hail to you, O blessed morn")——"Du som fromma hjärtan vårdar" ("Christians, while on Earth abiding") and "Vi lovar Dig, O Store Gud" ("We worship you, O God of might").
His style is described as melancholic but ravishing, often dealing with death, with frequent references and quotes from the Bible. His grand work was the long poem Angel of Death, finished only about year before his death. Compared to Swedish poets contemporary with Wallin, some consider him second only to Esaias Tegnér.