Niklas Sundin (born 13 August 1974) is a Swedish musician, best known as a founding member and former lead guitarist of the melodic death metal band Dark Tranquillity from 1989–2020.

In 2019, he founded his own band called Mitochondrial Sun, which has released two full-length studio albums to date.

He also wrote some of the lyrics for the first three and recent two Dark Tranquillity albums (Lead singer Mikael Stanne wrote all of Dark Tranquillity's lyrics from Projector through Fiction) and In Flames' album The Jester Race, and continued to translate In Flames vocalist Anders Fridén's lyrics from Swedish to English for the next few albums while Anders worked to become more proficient in English.

Sundin is also the founder of Cabin Fever Media, which among other things creates artwork for metal bands.

He previously used Rocktron Chameleon rack mounted pre-amplifiers, but after the Damage Done tour, he and Martin Henriksson began using Peavey 5150 and Mesa/Boogie Dual Rectifier amplifiers along with Behringer V-AMP 2 modeling processors.