From Longman Dictionary of Contemporary Englishtake it upon/on yourself to do somethingtake it upon/on yourself to do somethingformal to decide to do something without getting someone’s permission or approval first Reg took it upon himself to hand the press a list of names. → take
Examples from the Corpus
take it upon/on yourself to do something• Sir Herbert Morgan took it upon himself to act as chairman of an unofficial committee to help realise the three-year project.• He might be unwelcome, but he had taken it upon himself to come on over the first moment he heard.• He didn't dare take it upon himself to enlighten her further.• Many problems can be prevented if you take it upon yourself to keep the lines of communication clear.• Pius took it upon himself to proclaim the Dogma of the Assumption.• It is a dangerous path, however, when the executive takes it upon itself to qualify Parliament's decisions.• If we want our children to know certain information, perhaps we should take it upon ourselves to teach them.• So I took it upon myself to tell her, old nosey-parker that I am. 