Short answer. Yes, but only until contradicted. The Rules presume that official duty has been regularly performed. It is a disputable presumption, so it stands where nothing is offered against it and gives way once evidence shows the officer departed from what the duty required.
What the law says
That official duty has been regularly performed
Rule 131, Section 3 — Disputable presumptions. Read the full provision →
What the law says
The following presumptions are satisfactory if uncontradicted, but may be contradicted and overcome by other evidence
Rule 131, Section 3 — Disputable presumptions. Read the full provision →
The presumption of regularity
Section 3 of Rule 131 includes among its disputable presumptions the presumption that official duty has been regularly performed. Its function is administrative rather than protective. Public business would be unworkable if every official act had to be independently proved correct before a court would look at it, so the Rules start from the assumption that officers did what their duties required. That starting point applies to the routine acts of public office generally, and it is why a party challenging an official act is the one expected to say what went wrong.
Two companion presumptions
The same list carries two related presumptions worth knowing about. One is that a person acting in a public office was regularly appointed or elected to it, so the officer's authority is not ordinarily an open question in every proceeding. The other is that a court, or a judge acting as such, whether in the Philippines or elsewhere, was acting in the lawful exercise of jurisdiction. Together with the presumption of regular performance, these keep proceedings from collapsing into arguments about whether officials and courts were properly constituted.
It is a presumption, not a conclusion
The heading matters as much as the clause. These presumptions are satisfactory if uncontradicted, but may be contradicted and overcome by other evidence. So the presumption of regularity is a rule about where a court begins, not a rule about how it must end. It does not immunise an official act from scrutiny, and it does not survive contrary evidence merely because the actor holds public office. Where the record itself shows a departure from what the duty required, the presumption has nothing left to support.
What this means if you suspect an irregularity
The burden is on the party alleging the irregularity, and it is met with specifics rather than suspicion. That means identifying the duty in question, showing what the officer was required to do, and showing what was actually done or omitted. Documents generated by the process itself are often the most useful, because they are the officer's own record of the steps taken. If you believe a public officer departed from a required step in a matter affecting you, take the paperwork to counsel promptly, while records and recollections are still available.