English Translation
He has already finished his homework.
Doesn’t しまった imply something bad, or is there a different context/ meaning here?
@TisYanni
As you guessed, しまった can be interpreted as a bad/inconvenient situation. 彼はもう宿題をやってしまった can be followed by “so, he has nothing else to do to kill his time at this moment.”
Another connotation of しまった is a present perfect tense (“have already done and what’s done is done.”)
To avoid the ambiguity, we usually say
彼はもう宿題をやり終えた。(しゅくだいをやりおえた)
彼はもう宿題を済ませている。(しゅくだいをすませている)
instead of 宿題をやってしまった.
A typical mom always ask her kid by saying 宿題終わったの or 宿題済ませたの？ These are common phrases.