Lay was born in Changsha, Hunan, China on October 7, 1991. His first known acting role was at six years old, starring as Huan Huan in the 1998 Chinese television drama We The People. In 2000, at nine years old, Lay participated in a Chinese TV show as a fan club member of the Taiwanese singer and actor Jimmy Lin, giving him his first contact with the entertainment industry. Lay began his career as a local child star after winning third place in a competition organized by the Hunan-based TV show Star Academy in 2005. He also appeared in an episode of Yue Ce Yue Xin Kai and Liu Na's variety show, Na Ke Bu Yi Yang between 2005 and 2006. In April 2006, he auditioned for a leading part in Zhang Jizhong's The Duke of Mount Deer, but did not win the role despite being a finalist.

In 2008, Lay auditioned for S.M. Entertainment at the company's global casting auditions in Changsha. At the time of the auditions, he was 16 years old and studying at the High School Attached to Hunan Normal University, where he was featured as an outstanding student for his achievements. After successfully passing the auditions, Lay moved to South Korea for his idol training. In 2011, prior to his debut with Exo, he briefly worked with Shinee during their Shinee World concert tour as Jonghyun's dance replacement.

In December 2012, Lay was featured in S.M. Entertainment's project dance group S.M. The Performance featuring SM's best Dancers, alongside fellow Exo member Kai and labelmates Yunho, Eunhyuk, Donghae, Minho and Taemin. On December 29, the group performed their single "Spectrum", which was released the following day, at the 2012 SBS Gayo Daejeon. As his group gained commercial success, EXO's studio album XOXO (album) became the first album to sell more than a million copies in South Korea in 12 years. Their 2014 album Overdose (EP) had even entered US Billboard's 200 chart.

Early in 2014, Lay composed and performed the song "I'm Lay" for his solo performance during Exo's first headlining concert tour The Lost Planet. Later in 2014, he performed another self-composed song titled "I'm Coming" on a special year-end television program on Hunan TV.

In February 2015, Lay participated in the "Return Home with Love for A Thousand Miles", a large-scale public welfare activities and volunteer project. The project included on-site delivery of relief supplies to labour workers which helps them return home faster and to help labour workers in a timely manner to reinforce physical safety. On May 2, Lay established his own foundation entitled, "Zhang Yixing Arts Scholarship" on behalf of providing scholarship for his alma mater middle school, Hunan Masters College Middle School where he will donate 100 thousand yuan annually. His intentions were encourage talented youth to pursue their dreams. On September 7, Lay responded to a campus soccer public welfare project, "Summit of Hope" (“希望之颠”). He uploaded a video on his Weibo account in an attempt to publicise the project.

On February 1, 2016, Lay donated an undisclosed amount to a joint Weibo public welfare funding project (#一起9加1#) which aids impoverished families for the upcoming Lunar New Year. In March 2016, in the second season of Go Fighting!, Yixing and the other cast members visited a community-run migrant worker dependent school located in Chuansha Xin Town of Shanghai as part of the "Go Fighting Welfare Development Project" (“极限公益成长计划”). The initiative donated more than 1.2 million yuan worth of materials for over 12 schools nationwide. On May 1, Lay participated in the Youku "Go Fighting Minute Challenge" public welfare project on Weibo where he sent greetings to as many friends and families as possible in one minute and urged the public to express positive Energy and to donate to charity. With previously having his own foundation established, he further donated another 1 million yuan and a piano to his alma mater. Later that year, in conjunction with the 10th anniversary of his alma mater, Yixing once more donated another 1 million yuan of fund to his scholarship foundation. On July 2, Lay was honourably appointed as the Publicity Ambassador of the Communist Youth League of China (CYLC), expressed that he will dedicate himself to his appointment and appealed to the public to do charity through singing the national anthem. On September 9, Lay attended the 2016 BAZAAR Stars’ Charity Night which resulted in him donating 10 ambulances with worth amounting to 700 thousand yuan. Due to his charitable contributions, Lay was ranked number 15th by the China Philanthropist Magazine in the '2016 China's Top Philanthropist Celebrity List'.

On September 9, 2017, Yixing attended the 2017 BAZAAR Stars’ Charity Night and donated 15 ambulances, valued at 1.05 million yuan. In January 2018, he starred in a public welfare movie (我在你身边) in which he sang and composed the theme song too. On March 30, 2018, he starred as a guest recitalist in CCTV's Trust in China talk show.

On December 22, Lay released his second extended play Winter Special Gift on QQ Music and KuGou app. The music video of the lead song for the album, "Goodbye Christmas" was also released concurrently on the same day. Within one day of digital sales, the album broke four records of Gold, Double Gold, Triple Gold and Platinum on QQ Music. The album later broke Diamond record on QQ Music. On December 28, Lay was announced to be starring as a supporting role in Empress of China which is scheduled to air on Jiangsu TV and Youku in 2019.