Custodian of the Two Holy Mosques King Abdullah has appointed Prince Naif as the Crown Prince and deputy premier, the Royal Court statement said late Thursday.
Prince Naif was the second deputy premier and interior minister in the Council of Ministers.
He will continue to head the Interior Ministry along with his new positions.
Prince Naif, who has been the second deputy premier since 2009, was born in Taif in 1933 as the 23rd son of the founder of the Kingdom - King Abdul Aziz.
He was educated in the princes' school, in addition to receiving instruction from his father and eminent religious leaders.
Prince Naif began his political career as deputy governor of Riyadh and later became the region's governor during the lifetime of King Abdul Aziz.
King Faisal appointed Prince Naif deputy minister of Interior in 1970.
Four years later, the prince became deputy minister of interior with the rank of minister.
King Khaled appointed Prince Naif as minister of state for Internal Affairs in 1975, and later in the same year, was named the minister of interior, a position in which he continued to serve till his appointment as crown prince and deputy premier on Friday.
Earlier, King Abdullah bin Abdul Aziz held a meeting with the chief and members of the Allegiance-Pledge Commission at his palace in Riyadh.
During the meeting, Prince Abdullah bin Faisal bin Turki al-Awwal (the first) bin Abdulaziz Al Saud and Prince Bandar bin Musaed bin Abdulaziz al-Saud were sworn in before the monarch as new members of the Commission, according to Saudi Press Agency.
The agency added that the new commission members pledged of allegiance to Prince Naif and "wished him every success and to become the best assistant to the Custodian of the Two Holy Mosques and the Kingdom of Saudi Arabia steady security, stability and national integration.
" Prince Naif was widely thought to be next in line after Prince Sultan, who was named second-deputy prime minister in 2009.
King Abdullah has been seen as a reformer, making incremental changes to improve the position of women, for example, and to modernize the kingdom despite some backlash from ultra-conservative clerics.