The major purpose of the study was to investigate the effect of Think-Pair-Share instructional Strategy on secondary school students' achievement in Civic Education in Bayelsa State, Nigeria. The study adopted a quasi-experimental 2x2x3 pre-test,-post-test factorial design. All the SSS II students in Bayelsa State constituted the target population. Intact classes of 61 and 46 students were purposively sampled for the experimental and control groups respectively. Three researcher-designed instruments which included two instructional packages and one Test were used to collect data for the study. Reliability index of the Civic Education Achievement Test was 0.83 obtained through a test re-test method after an interval of two weeks using Pearson's Product Moment Correlation while Analysis of Co-variance (ANCOVA) statistic was used to test three research hypotheses at 0.05 level of significance. Findings from this study revealed among others that students taught Civic Education using Think-Pair-Share strategy outperformed those in the control group. There is no significant effect of treatments on secondary school students' achievement in Civic Education based on gender. Based on the findings, the study recommended among others that teachers should engage all categories of students in active learning where students' previous experiences are explored to recreate new knowledge.