Their musical style is characterized by their use of melodic guitar riffs and singing which shifts between growls and shouting.

Their music has been called winter metal since Immortal Souls utilizes frosty metaphors in their lyrics and usually creates a cold, wintry atmosphere.

At the end of January 1995 the band recorded a demo tape called Immortal Souls, which included six songs.

Also songs "Hate Sender", "I am Me" and "Realm of Hatred" were later published on the Once Upon A Time In The North compilation album as remastered versions.

In 2000, Pete Loisa (rhythm guitar) joined the group when the band was preparing to record their first full-length studio album.

After the tour Immortal Souls started to write new material and in November 2002 they went to Studio Sonic Pump to record the next album called Ice Upon the Night.

The band found a new drummer from their circle of friends in early 2005, when Juha Kronqvist joined Immortal Souls.

Because the Immortal Souls recordings had been long sold out, Fear Dark decided to publish them as remastered versions on the Once Upon A Time In The North 2 CD compilation album at the end of 2005.

Immortal Souls' music is typically fast, technical melodic death metal of Scandinavian school.

The lead guitar solos sets as a part of the accompaniment in both singing and virtuoso riffs and fast playing techniques.

The lead guitarist Esa Särkioja usually performs "darkly melodic riffage with power metal undercurrents".