A judgment void for want of jurisdiction is no judgment at all. It cannot be the source of any right or the creator of any obligation. All acts performed pursuant to it and all claims emanating from it have no legal effect. Hence, it can never become final, and any writ of execution based on it is void. It may be said to be a lawless thing that can be treated as an outlaw and slain on sight, or ignored wherever and whenever it exhibits its head.

JOANIE SURPOSA UY, PETITIONER, VS. JOSE NGO CHUA, RESPONDENT. G.R. No. 183965, September 18, 2009.

“x x x.

Neither can it be said that RTC-Branch 9, by approving the Compromise Agreement, in its Decision dated 21 February 2000 in Special Proceeding No. 8830-CEB, already made said contract valid and legal. Obviously, it would already be beyond the jurisdiction of RTC-Branch 9 to legalize what is illegal. RTC-Branch 9 had no authority to approve and give effect to a Compromise Agreement that was contrary to law and public policy, even if said contract was executed and submitted for approval by both parties. RTC-Branch 9 would not be competent, under any circumstances, to grant the approval of the said Compromise Agreement. No court can allow itself to be used as a tool to circumvent the explicit prohibition under Article 2035 of the Civil Code. The following quote in Francisco v. Zandueta⁠12 is relevant herein:

It is a universal rule of law that parties cannot, by consent, give a court, as such, jurisdiction in a matter which is excluded by the laws of the land. In such a case the question is not whether a competent court has obtained jurisdiction of a party triable before it, but whether the court itself is competent under any circumstances to adjudicate a claim against the defendant. And where there is want of jurisdiction of the subject-matter, a judgment is void as to all persons, and consent of parties can never impart to it the vitality which a valid judgment derives from the sovereign state, the court being constituted, by express provision of law, as its agent to pronounce its decrees in controversies between its people. (7 R. C. L., 1039.)

A judgment void for want of jurisdiction is no judgment at all. It cannot be the source of any right or the creator of any obligation. All acts performed pursuant to it and all claims emanating from it have no legal effect. Hence, it can never become final, and any writ of execution based on it is void. It may be said to be a lawless thing that can be treated as an outlaw and slain on sight, or ignored wherever and whenever it exhibits its head.⁠13 

In sum, Special Proceeding No. 12562-CEB before RTC-Branch 24 is not barred by res judicata, since RTC-Branch 9 had no jurisdiction to approve, in its Decision dated 21 February 2000 in Special Proceeding No. 8830-CEB, petitioner and respondent’s Compromise Agreement, which was contrary to law and public policy; and, consequently, the Decision dated 21 February 2000 in Special Proceeding No. 8830-CEB, being null and void for having been rendered by RTC-Branch 9 without jurisdiction, could not have attained finality or been considered a judgment on the merits.

X x x.”