Leipheimer was one of 11 riders who testified against Armstrong to the United States Anti-Doping Agency, who have accused the United States Postal Service team of running "the most sophisticated, professionalised and successful doping programme that sport has ever seen".
A statement issued by Omega Pharma-Quick-Step read: "Omega Pharma-QuickStep Cycling Team announces that the contract with Mr Leipheimer has been terminated, effective immediately.
"We commend the rider for his open co-operation with USADA and contribution to cleaning up the sport of cycling. However, in the light of the disclosures made by Mr Leipheimer in his public statement on October 10, the team has decided to terminate the contract.
"This decision has the full support of the team owner, the board represented by Mr Bessel Kok and team manager Mr Patrick Lefevere."