Mswati III, 45, who retains immense power under the current system, kept on his prime minister despite opposition from key political players.
Dlamini, 71, was absent when the announcement was made, a departure from a tradition whereby the premier mixes with crowds around a cattleshed when the king unveils his name.
Mswati said that due to his vast political and economic experience, Dlamini was the "rightful candidate" to help Swaziland's economic recovery.
According to a recent report by the Central Bank of Swaziland, Swaziland's GDP growth declined from 0.7 percent in 2011 to 0.2 percent last year.
A former minister of finance, Dlamini first served as prime minister between 1996 and 2003. He was then re-appointed to the position in 2008.
Observers suggest that the king decided to retain his services because he is seen as a useful figure for battling riots and public protests.
Social upheaval is uncommon in Swaziland, and police have crushed the few peaceful protests organised in the country in past years.
Political parties are not uniformly banned, but cannot contest elections.
Voters chose 55 lawmakers during the September 20 elections, with candidates hand-picked by traditional chiefs loyal to the king.
Pro-democracy activist Jan Sithole, 60, won a seat in the elections, which were criticised by regional observers.
Sithole, leader of the Swaziland Democratic Party (Swadepa) and a vocal critic of the current political set-up, vowed to change the government from the inside.
"I am looking forward to working with the appointed prime minister in building the country's status," he said.