Usage patterns
〈人〉が職務を遂行するfor someone to carry out their official duties
The police officer calmly carried out his duties.
〈人〉が職務を怠るfor someone to neglect their duties
He was warned by his boss for neglecting his duties.
〈人〉が職務を全うするfor someone to fulfill their duties completely
She fulfilled her duties completely to the very end.
〈人〉が職務に励むfor someone to devote themselves diligently to their duties
The new employee is diligently applying himself to his duties.
Expressions
職務上in the course of one's duties; in an official capacity