The film was described by critics as gritty, forlorn, honest and realistic as well as a pacifist piece confronting less pleasant sides of Finnish history.

The film's setting is based on the unit Väinö Linna served in during the Continuation War, Infantry Regiment 8 (Finnish: Jalkaväkirykmentti 8).

[7][11] The film occasionally shifts to the homefront, showing for example the company's commander Kariluoto marrying his fiancée at Helsinki Cathedral in the midst of war and corporal Antero Rokka visiting his wife Lyyti and children at their farm on the Karelian Isthmus.

Lahtinen is killed during a Soviet breakthrough, but Rokka halts a flanking 50-strong enemy unit by ambushing them with a Suomi KP/-31 submachine gun from high ground.

The soldiers drink kilju (a home-made sugar wine) until intoxication during Commander-in-Chief Field Marshal Carl Gustaf Emil Mannerheim's birthday celebrations, a new recruit is killed by a sniper and replacements reinforce the company.

In the subsequent fighting, the company suffers large numbers of casualties, including Captain Kariluoto, and abandons its machine guns during a retreat from a hopeless defence.

The soldiers rise from their defensive fighting positions after the final Soviet artillery barrage stops and they listen to the first radio announcements on the eventual Moscow Armistice.

[11][25] The film was produced by the Finnish Elokuvaosakeyhtiö Suomi 2017 with the Icelandic Kvikmyndafélag Íslands and Belgian Scope Pictures as co-producers.

[10][20][28][21] The soundtrack of the film was composed by Lasse Enersen (with whom Louhimies had cooperated before) and recorded with the Lahti Symphony Orchestra at Sibelius Hall.

Louhimies wanted the music to display "soul and fragility"[33] while Enersen described it as "simple, stark, sometimes raw and ugly"[34] and left out themes of heroism or victory from the score.

[12][38] Director Louhimies commented that he intended to highlight the individuals taking part in war instead of glorifying conflict and stay true to Väinö Linna's views.

However, the film was described as using Russian actors, such as Diana Pozharskaya playing Vera in the conquered Petrozavodsk, to humanize the war.

[41] It opened at the Subtitle film festival in Ireland on 25 November 2017,[42] in Sweden on 6 December 2017,[43] in Iceland on 25 January 2018[44] and in Norway on 9 February 2018.

It broke the record for the biggest opening weekend for a Finnish-language film and settled overall third after Star Wars: The Force Awakens and Spectre.

[48] Marko Ahonen from the newspaper Keskisuomalainen appraised The Unknown Soldier with five out of five, describing it as "an impressive pacifist war film" where the reality of combat is forlorn and unpleasant.

[12] Hufvudstadsbladet's Krister Uggeldahl called it "as traditional as respectful" and "a movie that breathes and lives (even when death is harvesting its victims), but at no stage apologizes" and gave it four out of five while thanking the actors' complete work.

According to Typpö, the film was not bold enough, and instead followed conventional depictions of masculinity in Finnish cinema and was a safe, risk-free attempt to please everyone under Finland's 100 year celebrations.

[43] Björn Jansson from Sveriges Radio said the film is "a good depiction of the war's meaninglessness and insecurity" but that it is difficult to get along with its "futility, emptiness and waiting in muddy trenches", rating it three out of five.

[54] Extended footage from the 2017 Tuntematon sotilas film was edited into a five part TV series totaling 4 hours and 30 minutes.