Barrasso is a Republican like Thomas, meaning the appointment will have no effect on the U.S. Senate's party breakdown. A staunch supporter of anti-abortion causes, limited government, lower taxes and a strong national defense, he is considered politically conservative.
Telephone messages left with Barrasso were not immediately returned.
Barrasso, an orthopedic surgeon from Casper, will serve until the beginning of 2009. A special election in November 2008 will decide who will finish Thomas' term, which runs to January 2013.
Barrasso's appointment is effective immediately.
while being treated for leukemia.
Freudenthal, a Democrat, chose Barrasso over Cheyenne attorney Tom Sansonetti and former state Treasurer Cynthia Lummis. The Wyoming Republican Central Committee had nominated the three after 31 people applied for the job.
"There are many factors that went into this decision, and it was the sum of these factors that led me to this choice," Freudenthal said in a statement. "While I don't intend to indulge the speculation on why I made this decision, I will say that I hope I made the right choice."
Barrasso, 54, has been a state senator since 2003. He rose quickly in legislative stature, becoming chairman of the Senate Transportation, Highway and Military Affairs Committee.
However, his one attempt for a statewide office failed in 1996 when he lost in the Republican primary to Mike Enzi for the U.S. Senate seat vacated by Alan Simpson. Enzi eventually won the seat and is now the state's senior senator.
Barrasso said on his application for seat that he intended to run in the 2008 election for the remainder of Thomas' term.
And he leaves he no doubts that he will be a conservative voice in Washington for a traditionally conservative state.
"I believe in limited government, lower taxes, less spending, traditional family values, local control and a strong national defense," he said in his application. "In the state Senate, in addition to receiving an 'A' rating from the NRA, I have voted for prayer in schools, against gay marriage and have sponsored legislation to protect the sanctity of life."