He hailed from Zhuojun 涿郡 (modern Suning 肅寧, Hebei) and was a petty official in the local administration before he was recommended as appointee. He was made magistrate (ling 令) of Yangdi 陽翟, later on he became metropolitan commandant (jingfu duwei 京輔都尉) and then rose to the post of metropolitan magistrate (jingzhao yin 京兆尹). He is therefore also known as "Metropolitan Zhao", Zhao Jingzhao 趙京兆.
After the death of Emperor Zhao 漢昭帝 (r. 87-74 BCE) he participated in the downthrow of the incompetent emperor Liu He 劉賀 and the enthronement of Emperor Xuan 漢宣帝 (r. 74-49 BCE). Zhao Guanghan was for this support rewarded with the title of Marquis within the passes (guanneihou 關內侯) and appointed governor (taishou 太守) of the commandery of Yingchuan 潁川. In 72 BCE he participated in Zhao Chongguo's 趙充國 campaign against the steppe federation of the Xiongnu 匈奴.