adverb
Used adverbially to state that something applies to all cases or members of a group, with no exclusions.
この規則は例外なく全員に適用されます。
This rule applies to everyone without exception.
彼は例外なく毎朝ジョギングをする。
He goes jogging every morning without exception.
必ず means 'always' or 'without fail', focusing on certainty; 例外なく emphasizes that there are no exceptions to a rule or pattern.
Compound of 例外 (exception) + なく (adverbial form of ない, 'not'). Literally 'with no exceptions'.