Kuwait's Parliament on Thursday endorsed veteran security chief Sheikh Meshal Al Sabah as Crown Prince after the new emir nominated him on Wednesday.
Sheikh Nawaf Al Sabah assumed office as emir following the death of his brother Sheikh Sabah Al Ahmad last week.
The Parliament said the appointment of Sheikh Meshal, another brother of the late emir, was approved unanimously.
Who is Sheikh Nawaf, Kuwait's new emir?
Speaking after receiving Parliament's endorsement, Sheikh Meshal described the death of Sheikh Sabah as a "loss for Arabs, Muslim national and the whole world", state news agency Kuna reported.
He thanked Sheikh Nawaf for selecting him as Crown Prince and pledged to focus on the interests of the country and citizens under the leadership of the new emir.
Sheikh Nawaf wished Sheikh Meshal success in his new role and said he had "great confidence" in him, when the Crown Prince visited Seif Palace to take the constitutional oath before the emir, Kuna reported.
Diplomats and analysts say that because of his low-key style and age, Sheikh Nawaf, 83, may delegate a larger portion of responsibilities to the Crown Prince.
Sheikh Meshal, 80, became deputy head of the National Guard in 2004 and previously served as head of State Security for 13 years.
Experts on Kuwait said he had in the past declined offers of senior positions, steering clear of political battles and public roles.
Sheikh Meshal's rise stands in contrast to some other Gulf states, most notably neighbouring Saudi Arabia, where ruling families are starting to give top jobs to younger princes.
Kuwait is due to hold a parliamentary election this year.
