[1] Edgren passed the officer's exam in Stockholm in 1860, and subsequently served during the American Civil War in the Union Army, where he entered the 99th New York Regiment as 2d lieutenant in January 1862.
[1] He resigned towards the end of 1863, went back to Sweden and took commission in the Värmland Regiment, in which he served from February 1864 until August 1870, having been adjutant from July 1869.
Hjalmar Edgren translated into English the works of noted Swedish writer Viktor Rydberg.
Hjalmar Edgren also translated published works from English into Swedish, most notably the poetry of Henry Wadsworth Longfellow—for example "Evangeline" (Göteborg, 1875)—and Alfred Tennyson.
In addition, the multi-lingual Edgren was the author of numerous books of grammar in several languages including German, French, Italian, Spanish and Sanskrit.
[6][7] Among his publications are a German and English Dictionary, with Prof. W. D. Whitney (New York and London, 1877); and works in Swedish on The Literature of America (Göteborg, 1878), The Public Schools and Colleges of the United States (Upsala, 1879), Swedish Literature in America (Sweden, 1883) and American Antiquities (1885).