Is The Devil is a Part-Timer Based on a Manga or Light Novel, and is it Finished?

The Devil is a Part-Timer began as a series of light novels. From there came a shonen manga, written once again by Satoshi Wagahara. The manga is ongoing but the light novel series is complete.

The Devil Is a Part-Timer Season 3 Confirmed, Trailer Released - Anime Corner

The Devil is a Part-Timer Season 3 Episode 3 Release Date & Time

Light Novel Volume 6, Hataraku Maou-sama! Wiki

The Devil is a Part Timer - Anime Review

It's awesome when animes do this, end the series with some event or quote from the beginning like OHSHC

I got the last volume of “the devil is a part-timer.” I enjoyed the journey and can't wait to read the last volume within this week. : r/LightNovels

The Devil is a Part-Timer!! 2nd Season (Sequel) Key Visual : r/anime

When Demon Lord Satan Jacob’s plans to conquer the world of Ente Isla are thwarted by hero Emilia Justina, he and his demon general Alciel escape

The Devil Is a Part-Timer! Vol. 0-II (Light Novel)

Light Novel Volume 17, Hataraku Maou-sama! Wiki

The Devil is a Part-Timer!! 2nd Season Receives New Trailer and Visual, Premiere Date

Hataraku Maou-sama!! (The Devil is a Part-Timer! Season 2)