Changes also announced in defence while finance and energy portfolios remain unchanged
Qatar's emir issued a decree on Wednesday replacing the foreign minister and merging some portfolios, state news agency QNA reported, in what was seen as a move to consolidate his power and cut costs after the sharp drop in oil prices.
Qatar, the world's biggest liquefied natural gas exporter, is one of the Gulf's richest countries, although the value of its energy exports almost halved last year.
The new foreign minister was named as Sheikh Mohammed bin Abdulrahman al-Thani. The ministers of energy and finance were unchanged.
Khalid al-Attiyah, the outgoing foreign minister, will become state minister for defence affairs.
The emir, Sheikh Tamim bin Hamad al-Thani, who took over in 2013 after his father stepped down, also holds the post of defence minister.
A Western diplomat in Doha said cost-cutting was one reason for the changes, following the sharp decline in oil prices.
The decree merged several ministries, including communication and transport and culture, youth and sports, heralding the possibility of many job cuts.
"But this is also about Sheikh Tamim's slow consolidation of power after 2-1/2 years in the job," the diplomat said.
"He's still pushing out the old timers loyal to the former emir who were not necessarily that effective but couldn't be sacked all in one go," the diplomat added.
The outgoing minister of state for defence affairs, Hamad bin Ali al-Attiyah, was appointed as an adviser to the emir with the rank of a prime minister, QNA said.
The public health minister was also replaced.