In 77 CE, he was appointed a court gentleman (lang 郎), then palace attendant (shizhong 侍中) and soon Leader of the Court Gentlemen Brave as Tigers (huben zhonglangjiang 虎賁中郎將). On the accession to the throne of Emperor He 漢和帝 (r. 88-105 CE), Dou Xian's sister Empress Dowager Dou 竇太后 took over regency (linchao chengzhi 臨朝稱制).
Dou Xian was one of the most important persons of the unofficial court of the female regent and took over the role of the official proclamation of edicts for his sister. Their other brothers Dou Du 竇篤, Dou Jing 竇景 and Dou Gui 竇瓌 were appointed to high positions. The Dou family therefore was the most powerful of the whole empire and was at the same time hated by others.
In 89 CE Dou Xian hired an assassin to kill a favourite of his sister, yet his crime came to light and he was incarcerated. In order to escape the death penalty, Dou Xian took over the lead of a campaign against the steppe federation of the Northern Xiongnu 匈奴. The Empress Dowager appointed him general of cavalary and chariots (cheji jiangjun 車騎將軍) and put the Chamberlain for the Imperial Insignia (zhijinwu 執金吾) Geng Bing 耿秉 at his side. Heading 4,000 cavarlymen and more than 30,000 auxiliary troops of Southern Xiongnu, Wuhuan 烏桓 and Qiang 羌, Dou Xian defeated the Xiongnu at Mt. Qiluo 稽落山 (modern Mt. Ebugen 額布根, Mongolia) and pursued the enemy far into the steppe. He climbed Mt. Yanran 燕然山 (modern Khangai Range in central Mongolia, Ch. Hang'aishan 杭愛山) where he erected a stele reporting his victory, and returned.
Back home, he was pardoned, given the title of General-in-chief (da jiangjun 大將軍) and appointed Grand Mentor (taifu 太傅) as head of the Three Dukes (sangong 三公). In the following year Dou Xian continued his efforts to crush the Northern Xiongnu. He established military agro-colonies (tuntian 屯田) in the western province of Liangzhou 涼州 (modern Gansu) and sent out Geng Kui 耿夔 to defend the northern border of the empire towards the steppe. On Mt. Jinwei 金微山 in the Altai Range, Dou Xian again defeated the Xiongnu khan and so brought an end to their federation.
Dou Xian's power had become so great by his successful campaigns that the court feared his influence and had the suspicion that Dou Xian planned to overthrow the Han dynasty. Emperor He therefore took measures to deprive Dou Xian of his power. The eunuch Zheng Zhong 鄭眾 was entrusted with the plot. When Dou Xian returned to the court in 92 CE the palace guard arrested him and his entourage. Without requesting that he give back his seal as general, Dou Xian was given the title of Marquis of Guanjun 冠軍侯 and ordered to leave the court to retire to his marquisate. Arrived in Guanjun, he received an imperial order to commit sucide.