The man's 78-year-old wife, who was also in the car, was transported to a hospital in good condition, ambulance officials said.
A group of people had gathered in southwest Oklahoma City to watch the installation of the steeple when the crane collapsed in the parking lot, said Deputy Fire Chief Cecil Clay.
Grace Assembly of God Pastor Joe Hancock said the couple were longtime church members.
"Just great people," he said. "It's just a huge loss."
Hancock said he was taking photos from the back of the church when he realized something had gone wrong. The crane started to tip when the steeple was about 10 feet off the ground, he said.
Caleb Fellenstein, the church's youth minister, said the crane started to lower the steeple just before the accident.
"And then it just quickened," he said. "The whole boom and the crane just flipped over. It was like a movie. It was like something unreal.
"I was just standing there in disbelief and panic."
The boom of the portable crane came to rest on the car, the smashed white steeple still attached.
The operator of the crane was not injured.
The woman was in the back seat of the car and the man was in the front passenger seat, said Lara O'Leary, spokeswoman for the Emergency Medical Services Authority, which operates emergency transport for the area. The couple's names weren't immediately released.
The Occupational Safety and Health Administration, the state Labor Department and the owner of the crane, Barnhart Crane and Rigging Co., were to investigate.
Jeff Latture, Barnhart senior vice president, said it had been years since the company had an accident.
"We do about 10,000 jobs a year without incident," he said. "We are very upset about this and certainly are concerned about families involved."
Latture said the cause of the accident will likely be a structural failure of the 90-ton crane, some kind of a problem with the ground it was sitting on, or operator error.
"It was at the beginning of a very simple lift, which is somewhat troubling to us and not far into the lift when the crane went over," he said.
Clay, the fire official, said he saw no obvious equipment failure or problems with the ground the crane was on.
Latture said about 150 feet of the telescoping boom was deployed at the time of the accident.
There have been several deadly crane accidents around the country this year, including one in Houston last week that killed four workers and injured seven others. Crane-related deaths have also occurred in New York, Miami and Las Vegas.
An Associated Press analysis in June found that cities and states have wildly varying rules governing construction cranes.
Cranes in Oklahoma fall under OSHA regulations but operate without any state oversight, state Labor Commissioner Lloyd Fields said. He said Oklahoma may join other states considering improved regulatory oversight of cranes. Oklahoma is among 35 states that do not require crane operators to be licensed.