英语翻译该同学在本科阶段先后担任了团支部和党支部的职务,尽职尽责,与老师同学相处融洽.

The student served as the Secretary of League Branch and the Secretary of CCP(Chinese * Party) Branch during his （或者her) undergraduate study period, fulfilling his (或者her) responsibilities of these two duties. and enjoying harmonous relations with both teachers and classmates.
括号内的是帮助你理解的,（Chinese * Party) 起解释说明作用,可以保留.其他两个括号你根据性别选好用his或her后去掉括号内容.