Old Law, Greenberg v. Brookshire, 640 S.W.2d 870, 871-872 (Tex. 1982):
... plaintiff has an absolute, unqualified right to take a non-suit upon timely motion as long as defendant has not made a claim for affirmative relief. ...
The granting of a non-suit is merely a ministerial act. A plaintiff's right thereto exists from the moment a written motion is filed or an oral motion is made in open court unless the defendant has, prior to that time, filed pleadings seeking affirmative relief.
“The right to take a non-suit is governed by Rule 164.” Corder v. Corder, 189 S.W.2d 100, 101 (Tex.Civ.App.-El Paso 1945, writ ref'd). The rule is plain. Kidd v. McCracken, 105 Tex. 383, 150 S.W. 885 (1912). Until 1975, Rule 164 represented a verbatim adoption of what had been Art. 2182 FN1 and its predecessors dating back to 1853. 1853 Tex.Gen.Laws, ch. 11, § 99, at 19; 3 H. GAMMEL, LAWS OF TEXAS 1303 (1898). See Historical Note, Tex.R.Civ.Pro.Ann. Rule 164 (Vernon 1979). In Hoodless v. Winter, 80 Tex. 638, 16 S.W. 427 (1891), this Court construed a predecessor to Rule 164, stating:
FN1. Statutory references are to Tex.Rev.Civ.Stat.Ann. (Vernon's 1964).
The right of a plaintiff to take a non-suit upon his own cause of action was considered of sufficient importance by the legislature to be given express recognition.... [I]t is important that the substance, and not the shadow alone, of the right shall be preserved.... It is only when the defendant, by a counter-claim, seeks some “affirmative relief,” that the right of the plaintiff to discontinue the entire cause is forbidden.... The defendant must not only pray for affirmative relief, but he must state facts showing that he has a cause of action....
Rule 162:
Notice of the dismissal or non-suit shall be served in accordance with Rule 21a on any party who has answered or has been served with process without necessity of court order.
New Law, Crites v. Collins, 284 S.W.3d 839, 840 (Tex. 2009)(per curiam):
In this health care liability lawsuit, the plaintiffs voluntarily nonsuited their claims against the defendant health care provider after failing to serve a medical expert report within the 120-day deadline required by the Medical Liability Insurance Improvement Act (MLIIA). See Tex. Civ. Prac. & Rem.Code § 74.351. Before the trial court entered an order of nonsuit, the defendant filed a motion for dismissal with prejudice and for attorneys' fees and costs as sanctions for noncompliance with the expert report deadline.
A judgment dismissing all of a plaintiff's claims against a defendant, such as an order of nonsuit, does not necessarily dispose of any cross-actions, such as a motion for sanctions, unless specifically stated within the order.
In Crites, no counterclaim was on file when the non-suit was taken, and no order of non-suit is required by Rule 162. However, the Supreme Court now allows a counterclaim to be filed after notice of non-suit, if no order of non-suit is on file. The shadow alone of the right to non-suit is all that is left.
However, after Crites, the Supreme Court ruled that if you take a non-suit before the counterclaim is filed, the trial court must dismiss the case. In re Greater Houston Orthopaedic Specialists, Inc., 295 S.W.3d 323, 324-325 (Tex. 2009). Greater Houston Orthodpaedic even upheld a misnamed non-suit. Id., at 325.