They were killed by a bomb blast near Baghdad, just one of a wave of attacks in the Iraqi capital that also saw 14 Iraqis killed in a bus bombing.
Paul Douglas, 48, a veteran cameraman, and sound technician James Brolan, 42, both with CBS, died when their convoy was struck by an improvised explosive device.
Also killed in the attack were a US army captain and an Iraqi interpreter, according to the British Foreign Office.
CBS correspondent Kimberly Dozier, 39, who has both US and British citizenship, sustained heavy injuries in the attack, CBS said in a statement.
The attack was one of eight bombings that left dozens of people dead and wounded, in the worst wave of violence to hit the Iraqi capital in days.
The three journalists were reporting outside their "humvee" vehicle while on a mission embedded with the US 4th Infantry division and were believed to be wearing body armour when the bomb exploded, CBS said.
Ms Dozier was taken to a US military hospital in Baghdad where she underwent surgery, and her condition was described as "critical".
"This is a devastating loss for CBS News," said president Sean McManus. "Kimberly, Paul and James were veterans of war coverage who proved their bravery and dedication every single day."
Ms Dozier and her London-based team were the latest in a rising toll of journalists killed and wounded in the Iraq conflict.
In January US-network ABC News anchor Bob Woodruff and cameraman Doug Vogt suffered severe injuries in a roadside bombing in Iraq. Mr Woodruff is still recovering from serious head injuries and broken bones.
Mr Douglas had worked for CBS News since the 1990s in Afghanistan, Pakistan, Rwanda and Bosnia.
Mr Brolan, a freelancer, had worked for CBS for the past year in Iraq and Afghanistan, the network said.
The Paris-based Reporters Without Borders says Iraq is the world's most dangerous country for journalists.
At least 95 reporters and their assistants have now been killed since the US-led invasion in March 2003, the organisation says.
Reporters Without Borders also said at least 42 media workers have been kidnapped in Iraq since the war began, most of them Iraqis.
Upsurge in attacks
In the Iraqi capital, 14 people died and 17 were wounded when a bomb tore through a bus carrying Iraqis from Khalis, 80 kms north of Baghdad, to Camp Ashraf, the home of an Iranian opposition movement.
All the dead were workers at the Ashraf base of the Mujahedeen Khalq, or MEK, which opposes Iran's regime. The group, made up of Iranian dissidents living in Iraq, said the dead were Iraqi workers heading to their camp.
In other attacks, a car bomb near Baghdad's main Sunni Abu Hanifa mosque killed at least nine Iraqi civilians, hospital sources reported.
A bomb planted in a parked minivan killed at least seven when it exploded at the entrance to an open-air market in the northern Baghdad suburb of Kazimiyah.
Political impasse
Meanwhile Iraq's parliament debated the deteriorating security situation, but progress on the issue has been hampered by Prime Minister Nouri al-Maliki's inability to appoint the crucial defence and interior ministers, which control security forces.
The Shi'ite-dominated interior ministry, which controls the police forces, has been promised to that community. Sunni Arabs are to get the defence ministry, overseeing the army.
US officials hope Iraqis will be able to take over security duties over the next 18 months, allowing US forces to begin pulling out.