William, 24, will train to be a troop leader in an armored reconnaissance unit, just like his brother.
William is second in line to the throne behind his father, Prince Charles.
He will begin a six-month training course, which Harry is about to finish, at Bovington Camp in Dorset next year, Clarence House said.
After about a year in the Army, William will spend time with both the Royal Air Force and the Royal Navy on familiarization attachments, Clarence House said.
He will, at this point, carry out public engagements in parallel to his military career, and they will become more frequent as he approaches the end of his service.
"The prince will also aim to address the wider issues of preparing himself for his future roles — learning more about constitutional matters, charitable work and the organization and estate management," said the announcement from Clarence House, Prince Charles' official residence in London.
"Finally, Prince William will be further developing his ideas for his medium-term role following Army service, both in supporting the queen and the prince of Wales and in furthering his own charitable interests."
The Household Cavalry is a regular army unit, but it also supplies soldiers for ceremonial duties at Buckingham Palace and other venues.
The Blues and Royals were formed in 1969 from an amalgamation of the Royal Horse Guards (Blues) and The Royal Dragoons (1st Dragoons).