Commissioner Mike Geeslin, 41, said in a letter to Gov. Rick Perry that his decision was based on many considerations, but mostly it had to do with his family and a "simple realization that it is time for someone else to lead."
Geeslin's announcement comes just six days before the beginning of the legislative session.
"I wanted to wait until after the first of the year," he said. "With the new year comes change."
Perry praised Geeslin's work as commissioner, but he hasn't appointed a replacement, according to Perry spokeswoman Catherine Frazier .
Though Geeslin probably will not have to endure the usual hours of testifying before state lawmakers, he said he would stay with the department through the legislative session, if asked.
Under Geeslin's tenure, the Texas insurance market has grown from $78 billion to $102 billion. The department helped consumers collect more than $220 million in payments, and it took regulatory action — in the form of restitution and refunds — in excess of $800 million, most notably in a multimillion-dollar rate case involving State Farm Insurance.
"It's not really my legacy, and I cannot take credit for it," Geeslin said. "I have learned so much in working with these people here."
Some of the challenges Geeslin said he faced during his time as commissioner included dealing with the fallout of several major hurricanes, merging the Insurance Department with the Texas Workers' Compensation Commission and undergoing two consecutive Sunset Advisory Commission reviews, which are periodic examinations of state agencies to determine whether they should continue to exist.
Mark Hanna, a spokesman for the Insurance Council of Texas, an industry group, said Geeslin's successor will discover quickly how challenging the job of Texas insurance commissioner can be. Insurance commissioners in Texas need to be expert in a variety of areas, including windstorm issues and annuities, Hanna said.
"His successor will find out that being the insurance commissioner is one of the hardest and most difficult positions that you'll find in state government," Hanna said.
Alex Winslow, the executive director of the consumer advocacy group Texas Watch, said the state has a dysfunctional regulatory system with lax oversight. Now, he says, Perry has an opportunity to look to someone who would improve the insurance environment for Texans.
"The governor must appoint an insurance commissioner who will work every day for Texas families — not to fatten the insurance companies' already bloated profits," he said.
Geeslin chose not to respond to Winslow's statements.
Geeslin's advice to the next commissioner: Keep in mind that decisions made in the job are not confined to the borders of the state.
"The insurance world is much bigger than what it has been in the past," Geeslin said. "Texas is a player in the world market, and you have to look at this job as big."
Geeslin was an aide to Perry who specialized in insurance and regulatory matters before he served as deputy commissioner for policy at the Department of Insurance. Perry made him commissioner in 2005, when Geeslin was 36.