The Book of Isaiah is believed to have been written over several years spanning from 701 BC to 681 BC. The last 26 chapters are thought to have been written by Isaiah in his later years.
Some Biblical scholars do not believe that Isaiah wrote the entire book bearing his name, according to Biblica. However, no other authors have been attached to it. Other scholars argue that the continuity demonstrated throughout the book in the usage of the expression "the Holy One of Israel" is proof that he wrote the entire book, Biblica elaborates.
In addition to writing the Book of Isaiah, the prophet is also credited with writing the history of King Uzziah in 2 Chronicles 26.