The jury also noted that 51-year-old Pat Hughes was terminated as part of city retaliation for his complaints about age discrimination.
"I feel vindicated," said Hughes shortly after the decision. "I hope this sends a message to the city."
North Richland Hills Mayor Oscar Trevino called the decision a "disappointment."
"We stand behind the leadership of the Fire Department," Trevino said. "We will be looking at all the options for an appeal."
The jury deliberated about four hours over two days before reaching its decision in State District Court No. 48.
The city must also pay legal fees, estimated at about $300,000, Hughes' attorney said.
Hughes, a 25-year veteran of the department, was fired in July 2001, when he was 48. He will not rejoin the department but hopes to find work in fire service.
The jury's decision came after two weeks of testimony.
"I'm elated," said Chris Medlenka of Fort Worth, Hughes' attorney. "Pat has been under attack for the last three years. Now, a jury has said 'enough.' "
Susan Hutchison of Grapevine, another of Hughes' attorneys, said the jury believed Hughes from the beginning.
"In closing, we told the jury that they could only award $300,000 for mental anguish, but they came back with $400,000," Hutchison said. "They sent the message that the city was wrong."
Trevino said the city has policies against discrimination and retaliation.
"We still contend that there was no age discrimination or retaliation," Trevino said. "He was let go for business reasons."
If the city has to pay, officials would have to look at funding options and present them to the City Council, said Mary Edwards, a city spokeswoman. The city is self-insured.
Councilwoman Nancy Bielik said the city should move forward.
"A jury of 12 found in favor of Mr. Hughes. Perhaps it's time to drop the fight and pay Mr. Hughes, and get back to the business of running our city," she said.
City officials contended that Hughes actively opposed Fire Chief Andy Jones when he was hired to run the department in 1998. Hughes was a candidate for the position.
Hughes received two bad performance reviews in 2000 and 2001 that city officials said led to his firing. A police internal investigation concluded that the Fire Department did not discriminate against Hughes.
But the U.S. Equal Employment Opportunity Commission found that Hughes had been discriminated against because of his age.
Two other former fire officials also filed complaints with the EEOC claiming age discrimination. The EEOC also found that they had been discriminated against because of age.