KBR is being investigated by the US stock market regulator over allegations it paid bribes for Nigerian gas deals.
Halliburton said it had severed ties with Jack Stanley, who had worked as a consultant since retiring in December 2003, and another person, over Nigeria.
It said it believes they obtained "improper personal benefits" in Nigeria.
Halliburton said Mr Stanley and the other ex-employee, whom it did not name, had engaged in "violations of ...codes of business conduct".
The US Securities and Exchange Commission is investigating allegations that KBR and three other partner firms paid $180m (Â£99m) in bribes to win gas contracts.
Inquiries Go On
Announcing the end of its relationship with Mr Stanley, Halliburton said it "does not believe it has violated the Foreign Corrupt Practices Act", which outlaws bribes to win overseas business.
Halliburton said it was continuing to co-operate with the SEC and US Justice Department, and to conduct an internal investigation.
US Vice President Dick Cheney was head of oil services conglomerate Halliburton at the time.
Halliburton says it has become a political target and insists it did nothing wrong.
The Nigerian government ordered the investigation in February and lawyers have since been studying the payments.
Other partners in the Nigerian project in which KBR had a 25% stake include Technip of France, ENI of Italy, and Japan Gasoline.
All are being investigated.
The allegations focus on a $4bn Nigerian natural gas plant built in the 1990s by the four partners.
The payments were allegedly made to Nigerian officials.
Halliburton has in the recent past also been under fire for allegedly overcharging the government on contracts relating to the US invasion of Iraq.