During her tenure as empress, she served as a loyal assistant and honest advisor to her husband, Emperor Taizong.
It was written that the ancestors of Zhangsun family traced their origin to the Xianbei dynasty Northern Wei's founding emperor Emperor Taiwu of Northern Wei's 17th generation ancestor Tuoba Kuaili (拓拔儈立) — that their ancestor was Tuoba Kuali's third son, who took the surname Baba (拔拔), eventually changed to Zhangsun when Emperor Xiaowen of Northern Wei changed Xianbei surnames to Han surnames in 496.
Li Shimin was Tang's most capable general in its campaigns to reunite China following Sui's collapse, defeating the major enemies Xue Rengao the Emperor of Qin, Liu Wuzhou the Dingyang Khan, Wang Shichong the Emperor of Zheng, and Dou Jiande the Prince of Xia.
Princess Zhangsun was said to serve her father-in-law Emperor Gaozu carefully, forming friendships with his concubines which she would use to cover up the mistakes of her husband and his faction.
When Li Chengqian's wet nurse the Lady Sui'an stated that his palace lacked sufficient goods and requested more, she replied, "All a crown prince should worry about is not having enough virtues or enough fame.
Her influence over him was such that she interceded on behalf of condemned criminals and changed his harmful decisions with gentle counsel.
The chancellor Wei Zheng advised against it, pointing out that this was contrary to Emperor Ming of Han's observation that his sons should not be as honored as his brothers.
On another occasion, after Emperor Taizong returned from an imperial gathering, he was angry and yelled, "Let me find a chance to kill this country-bumpkin!"
Empress Zhangsun herself was said to suffer from severe asthma, and her conditions were exacerbated in 634 when she was ill, but nevertheless attended to Emperor Taizong when he was forced to wake up in the middle of the night and put on armor and weapons due to an emergency report by his brother-in-law, Chai Shao (柴紹) the Duke of Qiao.
By 636, her conditions were severe, and Li Chengqian suggested to her that, as the doctors appeared to have done everything they could, Emperor Taizong declare a general pardon and encourage commoners to become Buddhist or Taoist monks, to try to gain divine favor.
Empress Zhangsun, knowing that Emperor Taizong had long disapproved of Buddhism and Taoism and herself believing overuse of pardons to be improper, refused.
Li Chengqian instead told the idea to the chancellor Fang Xuanling, who reported it to Emperor Taizong.
After she died, the palace authorities submitted Empress Zhangsun's writings—a 10-volume compilation of the good deeds of ancient women titled Examples for Women (女則, Nü Ze), and a commentary criticizing Han dynasty's Empress Ma – to Emperor Taizong.
When Emperor Taizong read her works, he was greatly saddened, and he stated: He summoned Fang back to his chancellor position, and then he buried her with honors due an empress, but reduced the expenditures as much as possible, as she wished.
Empress Zhangsun produced seven children with Emperor Taizong: Consort Chen is portrayed by Hong Kong actress Margie Tsang in TVB's 1987 series The Grand Canal (大運河)