Written and performed by Ben Gibbard, it is an acoustic solo ballad, and was recorded in monaural with a single microphone and little editing.

Based on this passage, who wrote i will follow you into the dark? Let's think fast. Stream of consciousness:
To answer this question, we should know that: Written and performed by Ben Gibbard, it is an acoustic solo ballad, and was recorded in monaural with a single microphone and little editing. So the final answer is Ben Gibbard.