The Hong Kong-listed company will pay Yang $61,875 per year and offer equity rights with a value of $135,000 in return for attending board meetings and providing views.
Yang, 44, resigned from Yahoo's board last year when he also stepped down from the boards of Alibaba Group Holding and Yahoo! Japan.
Lenovo, the second-biggest smartphone vendor in China, is stepping up its expansion in the business.
In its October-to-December third quarter, Lenovo shipped 9.4 million phones, including 9 million smartphones, mainly in China where its smartphone business was profitable for the first time.