Promoters AEG Live failed to spot a string of "red flags" that should have made them refuse to hire Murray, convicted of involuntary manslaughter in 2011 over Jackson's death, said cardiologist Daniel Wohlgelernter.
Testifying in a Los Angeles court, he said the jailed doctor violated all medical rules by using the drug propofol, which should only be used in a hospital setting by a trained anesthetist, to help Jackson sleep.
"My opinion is that Conrad Murray repeatedly failed (to meet) the standard of care in his treatment of Michael Jackson," he told a trial where 82-year-old Katherine Jackson, the star's mother, is suing AEG Live for negligently hiring Murray.
Jackson died on June 25, 2009, from an overdose of propofol, administered by Murray to help the singer sleep after rehearsals in Los Angeles for a series of concerts in London and his planned "This is It" world tour.
Wohlgelernter said Murray made repeated mistakes, including leaving Jackson unattended, focusing on his heart rather than breathing when he found him apparently lifeless, and delaying calling 911.
"My opinion is that these departures from the standard of care... were a substantial factor in the death of Michael Jackson," said the senior cardiologist, brought as a witness by Katherine Jackson's lawyers.
But Murray should never have been allowed to care for Jackson, given his behavior and qualifications, he said.
Murray's readiness to close his regular medical practice in Las Vegas almost overnight and abandon patients for a promised $150,000 a month salary should also have signaled that something was not right.
In addition, Murray's request for a cardiopulmonary resuscitation (CPR) machine on the tour was odd, given that Jackson had no history of heart problems.
"All these items to me are red flags that point me to Dr. Murray not being the appropriate physician to take care of Michael Jackson," said Wohlgelernter.
Jackson's health problems were well known: he cut short his "Dangerous" tour in 1993 and announced he had a drug addiction, notably to painkillers following treatment for burns to the scalp suffered during a Pepsi advert in 1984.
Murray had no specialized training for such problems.
"For Michael Jackson, given that he had no history of heart disease... a cardiologist's experience and skills and credentials would not be appropriate.
"It's a mismatch, it's not what he needs," he said, adding: "My opinion is that Dr. Murray was not an appropriate choice to serve as Michael Jackson's physician on the 'This is It' tour."
"It's not the right doctor for this patient."
The trial continues Wednesday with testimony expected from Alif Sankey, an actress involved in the "This is It" production.