The current study aimed to sightsee the effectiveness of Mathematical knowledge for teaching (MKT) through lesson planning and technological pedagogical content knowledge (TPACK) on Rwandan mathematics tutors in teachers' training colleges. A quasi-experimental research design was used with a control and an experimental group. The experimental group received the intervention on developing MKT through the lesson plan and TPACK, while the control group used a standardized format lesson plan templates as their primary method for preparing instructional materials. In both groups, we analyzed 88 lesson plans in three stages (before, during, and after intervention). The collected lessons were analyzed using a standardized and validated Lesson Plan Analysis Protocol (LPAP). The result revealed that, before the intervention, teachers in both groups struggled with preparing an effective lesson, with an average of 57.8% and 54% in the control and experimental groups, respectively, indicating that the prepared lesson could not be effectively taught. During the intervention, tutors in the experimental group were facilitated to improve their lesson preparation. In this regard, the average was increased to 61.37% in the experimental group, compared to 57.67% in the control group. Moreover, the post-intervention results revealed significant divergence in the two groups' performance, with an average of 82.40% (indicating a very good lesson plan that can be taught) in the experimental group and 59.73% (a fair lesson plan) in the control group. The inferential results showed a statistically significant difference in lesson preparation between Mathematics tutors in the experimental and control groups (p < 0.05) in favor of the experimental group during and after intervention. The research underscores the need for educational stakeholders and continuous professional development organizers to incorporate TPACK in lesson planning during teacher training to promote a more comprehensive and forward-looking approach to tutor preparation.