Alexandre Vinokourov has agreed a three-year deal to move from T-Mobile to Spanish team Liberty Seguros.
The 31-year-old, who was fifth in this year's Tour de France, said he could no longer ride in the shadow of T-Mobile team leader Jan Ullrich.
"My goal is clear, I want to win the Tour de France, so I chose the team with the best arguments," the Kazakh rider told sports daily L'Equipe.
"It's the most organised and the most experienced team."
Vinokourov won two Tour stages this year, including the last one on the Champs-Elysees.
He finished third overall in 2003.
"They have the best riders in the mountains and are among the best in the team time trials. It was almost a natural choice," he said of Liberty Seguros.
"We have discussed my programme for 2006 - I've had the guarantee I will be able to fully focus on the Tour de France."
Vinokourov will lead his new team, along with Spain's Roberto Heras, with 29-year-old Kazakh rider Sergey Yakovlev following him from Germany-based T-Mobile.
"He has proven he is a tough competitor and a leader especially in the Tour de France, and throughout his whole career," team director Manolo Saiz told the Liberty Seguros website.
"As well as being a great leader he will be a great role model for the younger riders over the next three years.
"He will form a good partnership with Roberto Heras that will allow us to develop without putting too much pressure on our youngsters, who are our future.
"He doesn't come to replace anyone, simply to complement what we already have and strengthen the team."