In a statement released Friday, Rubio said he wants to spend more time with his family. He also announced he's taking a job with Chevron.
"After the birth of our second child, and wanting to be closer to my family, I came to the terms that my current career path wasn't allowing for the quality family time," Rubio told Eyewitness News on Friday by phone.
Rubio has two little daughters. The younger one has special needs.
"I'm so incredibly proud of my friend, Michael Rubio," Leticia Perez said. She's now serving as 5th District Kern County Supervisor, a job Rubio held from 2004 until his election to the state Senate in 2010.
Perez worked in Rubio's Senate office.
"The first words that Michael uttered to me were, 'Leticia, family is first,'" she related.
Perez called Rubio a mentor and guide and said she's not surprised by the sudden resignation.
"We certainly had some discussion," she said. "I could see through the years that the demands on him as senator were increasing,"
As for the timing, Rubio said the opportunity to work for Chevron happened now, and it's right as far as his work in the Legislature.
"I wanted to have this process completed before the Legislative year takes off, so that we avoid any perceived or real conflicts," he said.
According to his official release, Rubio will take up duties with Chevron as the manager of California government affairs.
"I was born and raised in Lost Hills, I'm very familiar with the oil industry," Rubio told Eyewitness News. "They share my view that we need to provide an opportunity for people to go to work and provide for their families."
Political consultant Stan Harper said Rubio could make valuable contributions in his new job, saying he could "open doors" for the oil industry.
Resigning from his current post, Rubio leaves the Democrats without their two-thirds super majority in the Senate. Harper called Rubio's departure a big vacancy.
"I'm surprised that the leadership in the Senate didn't try to talk him out of it, perhaps they did," Harper said.
In Sacramento, political analyst Steve Maviglio said the resignation has significant implications, starting with the loss of the super majority in the Senate.
"Now they have one less seat, and that puts them a little bit short of that," Maviglio said. "Makes it a little more difficult for budget issues and other issues. And, because he's a rising star, the Democrats are looking for people from that part of the state that are going to move into leadership positions, and he certainly was in a position to do that."
In these situations, the governor is supposed to call for a special election to fill the vacancy. Local Democrats said they can hold onto the 16th District Senate seat.
"It's a very safe Democratic seat," Tom Webster said. "We're not concerned about it not being a Democratic seat, or staying a Democratic seat." Webster's the treasurer for the Kern County Democrats.
He said they'll look for good candidates who can represent people in the community and the district.
The 16th State Senate District takes in parts of Kern, Kings, Tulare and Fresno County. Harper thinks some "mayors up north" might be interested in running. And doesn't discount Republicans.
"I think in special elections, the Republicans have a better get-out-the vote drive than the Democrats," Harper said. "I think Republicans could pick up this seat."
Rubio said, in his absence, his Senate staff will stay in the district and Capitol offices to respond to the needs of residents of the 16th State Senate District.
Rubio said he and his family will stay in Sacramento.
"Our youngest is in therapy four days a week," Rubio said, adding there are good services for her in the Sacramento area. "I'll tell you she's got incredible spirit and is the happiest, little 15-month-old that I've ever come across."
Rubio said he's set to start his new duties at Chevron on March 4.
"I just want to work for a well-respected company," Rubio said. "And be productive for them, and be there for my family."