In the mid-2260s, he was described as a young engineer.
In 2267, when the Enterprise first encountered the 21st century Earth colony ship Stephen Hawking, Darmer concurred with Montgomery Scott that the Enterprise would have no difficulty taking aboard personnel effects from Hawking. He and Scott weighed the time needed to rig a tow brace and repair its life support, with Scott concluding that it'd take a week.
Darmer was serving in engineering with Scott when the Meropean bio-mass sent a neural feedback pulse through the starship's phaser banks. Tthe attack knocked him unconscious and left him with a broken arm. (TOS novel: Across the Universe)