Justice Mookerjee held the following in Pulin Behari Das v. King Emperor, 16 CWN 1105.

The acts of officers de facto performed by them within the scope of their assumed official authority, in the interest of the public or third persons and not for their own benefit, are generally as valid and binding as if they were the acts of officers de jure. This stands confirmed, without any qualification or exception, by a long line of adjudications.

The earliest case on record I have been able to trace is to be found under the name of The Abbe de Fountaine decided in 1431. It is remarkable that the language used by Chief Justice Babington plainly indicates that the principles of the De Facto Doctrine were even then not entirely new. From this period the De Facto Doctrine rapidly spread in England, and became firmly established, as is clear from a long series of decisions dealing with its various features and expanding its principles to meet the requirements of diverse circumstances and different times.

The substance of the matter is that the De Facto Doctrine was introduced into the law as a matter of policy and necessity, to protect the interest of the public and the individual where those interests were involved in the official acts of persons exercising the duties of an office without being lawful officers.

The De Facto Doctrine as encapsulated above has been reiterated by this Court in Pushpadevi M. Jatia, (1987) 3 SCC 367.

Where an office exists under the law, it matters not how the appointment of the incumbent is made, so far as validity of its acts are concerned. It is enough that he is clothed with the insignia of the office, and exercises its powers and functions. The official acts of such persons are recognized as valid under the De Facto Doctrine, born of necessity and public policy to prevent needless confusion and endless mischief.

The De Facto Doctrine was reiterated yet again in Veerendra Kumar Gautam, (2016) 14 SCC 18.

It is no doubt well settled that the acts of the officers de facto performed by them within the scope of their assumed authority in the interest of the public or the third persons and not for their own benefits are generally held valid and binding as if they were the acts of the officers de jure. A reading of the said does not give an omnibus authority to hold that every illegal act or acts performed which smacks of very many illegalities and incongruities should be merely ignored and validated. It has to be kept in mind that even while applying the De Facto Doctrine whether such acts performed were aimed at the prevention of public and private mischief and for the protection of public and private interest.

– Hon’ble Justice Hemant Gupta, State of Telangana v. Sri Managipet, [Criminal Appeal No. 1662 of 2019].