Endeavour, which is written by Russell Lewis (Lewis, Cadfael), will explore the origins of the character, famed for his love of crosswords, classical music and real ale.
Evans, whose TV credits include The Take and Come Rain Come Shine, will play the younger version of the Oxford detective originally made famous to TV audiences by John Thaw.
"Morse as a young man is a wonderful character that I'm very excited to be playing. My hope is that we can compliment what's come before, by telling a great story, and telling it well," said Evans.
Endeavour will be part of the 25th anniversary celebrations of the first episode of Morse, which aired on ITV in 1987. Thaw went on to film 33 more stories over the next 13 years.
Based in 1965, the story will be based around a missing schoolgirl investigation that finds Morse back in Oxford, where he is sidelined and ignored by Detective Inspector Fred Thursday. Morse will have to face his demons and risk everything to find a truth "that will haunt him for the rest of his days".
Laura Mackie, director of ITV Drama, said: "Inspector Morse was a television institution and nearly 14 million people tuned in to watch the final episode in 2000 when Colin Dexter's eponymous hero died from a heart attack. Endeavour is a beautifully written story that not only provides many nods to Morse's unique character traits for fans but reunites many of the team behind the original series."
Colin Dexter, the author of the Morse novels, added: "Immortal was Endeavour Morse - End-eavour more shall be so!"
Colm McCarthy (Injustice, The Tudors) will direct the Mammoth Screen production.