The paper reports a study that focussed on investigating the effectiveness of Toulmin's argument pattern (TAP) within Think-Read-Group-Share-Reflect (TRGSR) scientific argumentation strategy on higher secondary students' critical thinking. A quasi-experimental, pretest-posttest-control group design was deployed. The subjects were 50 twelfth grade students. The experimental group was taught with TAP within TRGSR scientific argumentation strategy, and on the other hand, the control group was taught with the traditional teaching approach (regular way of teaching that happens in the school otherwise). To measure the critical thinking ability, Watson-Glaser critical thinking appraisal Form--S was administered to both groups as a pre- and a posttest. The test contained 40 items with 5 elements (inference, recognition of assumptions, deduction, interpretation, and evaluation of arguments). After a 9-week-long intervention, analysis of covariance findings showed that there was a significant difference on the students' critical thinking ability between experimental and control groups. The students who were exposed to TAP within TRGSR scientific argumentation strategy proved to improve the ability of critical thinking. TAP coupled with TRGSR scientific argumentation strategy is relatively more effective in developing critical thinking ability than the traditional teaching approach.