He is most known for his valiant defence of Jianping (建平; southwest of present-day Xiayi County, Henan) during Jin's conquest of Wu.
Lu Kang appreciated Wu Yan's talents, but because he had plucked him from obscurity, he could not promote him further out of fear that the other generals would disapprove.
The generals fled in fear when they saw the supposed madman, but Wu Yan remained calm and even defended himself with a small desk.
The generals present all praised his bravery, so Lu Kang was finally able to promote Wu Yan to important positions.
He brought a piece of the wood to the Wu emperor, Sun Hao, as evidence that Jin was planning an invasion, and to persuade him to reinforce the northwestern border.
However, Sun Hao ignored his warnings, so Wu Yan instead personally built iron chains as a barrier to prevent an eastward advance through the Yangtze.
In December, Lu Kang and his generals repelled Jin forces led by Yang Hu and quelled Bu Chan's rebellion.
The chains that Wu Yan had built caused some inconvenience for the Jin navy at first, but they were dealt with by Wang Jun, who melted them by sending rafts full of dummies soaked in oil and burning them.
Tao's death sparked a rebellion in Jiuzhen Commandery led by Zhao Zhi (趙祉) who ousted the Grand Administrator of Jiaozhou, but Wu Yan managed to quell the revolt.
Near the end of his life, Wu Yan requested to be replaced, so he was appointed as the Empress's Chamberlain (大長秋) before he died in office.
[11] His last known activity was in 307, when the general, Li Zhao (李釗) was sent to quell a tribal rebellion in Ningzhou (寧州, modern Yunnan and Guizhou) that had broken out the prior year.
However, one official, Yin Yu (尹虞), admonished the brothers for judging Wu Yan by his circumstances and ruthlessly slandering him for a minor disrespect.