PC Alex Rush, based in Brighton, was instantly dismissed at a disciplinary hearing at Sussex Police HQ, which he also failed to attend.
Chief Constable Giles York, who chaired it, said PC Rush's failure to continue working was also gross misconduct.
He said it showed "a clear disregard for his sworn duty to the public".
PC Rush, 38, was being investigated following an allegation of assault but informed Sussex Police that he intended to resign.
A force spokesman said he was advised that this was not permitted under police regulations but he gave notice that he would resign regardless.
A "fast-track" gross misconduct investigation was convened on 28 July after he stopped attending work.
In a statement, Sussex Police said: "He chose not to attend, and Insp Matt Webb, chairman of the Sussex Police Federation, representing him, said that PC Rush had taken a 'pragmatic view', and had admitted to the allegation. He was dismissed with immediate effect."
Mr York said in the statement: "The regulations were clearly changed to prevent officers escaping the responsibility of holding public office and being held to account for their actions in that office.
"I believe that the point-blank [refusal] PC Rush has taken to his duty as a serving police officer to be available for work and attend work, while he is still being paid by the public purse, falls well below the standards expected in Sussex Police and across policing nationally.
"This shows a clear disregard for his sworn duty to the public and his moral duty to his colleagues during such challenging times for policing nationally and in Sussex.
Police did not give details of the assault allegation.
A policeman accused of gross misconduct has been sacked for refusing to continue reporting for duty after he knew he was under investigation.