It was either grad school or this: a seat on Berkeley City Council.

This is what’s playing out for 22-year-old Rigel Robinson. Just seven months after receiving his diploma in political science from UC Berkeley, Robinson is swapping out a master’s thesis for a more practical application of his degree.

“If not this, I’d probably be preparing for the LSAT,” he said.

Robinson joined a surge of young people who took part in the midterm elections, both as voters and candidates. When he’s sworn in Dec. 8, he’ll become the youngest council member in Berkeley’s history.

An estimated 31 percent of eligible voters ages 18 to 29 cast ballots this fall, according to the Center for Information and Research on Civic Learning and Engagement at Tufts University. That’s a 10-point bump from 2014 and marks the highest youth turnout in a midterm election in the past quarter century.

Young people also turned up on ballots as candidates, with considerable success. Come January, at least 26 House members will be Millennials, people ages 22 to 37, according to the Pew Research Center. All but six are freshmen, meaning that more than one-fifth of the 91 newly elected representatives are Millennials.

Robinson isn’t thinking about Congress just yet, though. He’s focusing on his first job in the professional world.

“In many ways, that’s a little ridiculous,” he said. “It’s kind of a punch line for me and all my friends, but at the same time, our campaign was elected because I was a qualified candidate.”

Robinson, who was external affairs vice president on UC Berkeley’s student government and served on the University of California’s Student Association, said he decided to run for the City Council after a 2014 redistricting created a south-side council district that was 86 percent students. Rigel and his peers at UC Berkeley resolved that with a supermajority of students, it was time for a student to run.

“I never really had a chance to consider for myself whether it should be me. Other people told me it should be me,” Robinson said. “At first I didn’t take it seriously.”

He added, laughing, “I guess I answered the call.”

But it was a fit for Robinson, both for his experience in student government and his affection for his new home of Berkeley, a “laboratory for democracy,” after growing up in St. Louis.

“We have the momentum to try things and get away with things that it’s not possible to do in other places,” Robinson said. “In a place like St. Louis, there isn’t necessarily the political capital to implement these changes unless other cities implement them first.”

Robinson announced his candidacy in April, almost three moths before longtime Councilman Kriss Worthington announced his plans to retire. Shortly before, Worthington began reaching out to Robinson for what turned out to be a series of quasi job interviews.

“He gave me a string of calls, very reliably very late at night,” Robinson said. “I think Kriss just had a very high threshold for compatibility for whoever his next successor would be.”

Even though his district on the south side of campus is dominated by students, Robinson said he sometimes struggled to get voters to take him seriously.

For every person who thanked him for running, he said, “there were people who told me they were skeptical of me.”

So those were the ones he concentrated on, said his campaign manager, 20-year-old UC Berkeley junior Varsha Sarveshwar. The campaign identified precincts with more long-term residents than students, and Robinson went there regularly to talk with voters.

“We were very, very cognizant of that concern,” Sarveshwar said. “We had him knocking on those doors most frequently.”

In the style of a more seasoned candidate, Robinson would steer conversations away from his age and toward his platform, which emphasized affordable housing and improved relations between students and long-term residents. He also knew better than to play up his youth.

That would have been “purely counterproductive, because so many people didn’t want to elect this child to City Council,” he said.

For hard-core skeptics, Robinson gave out his personal phone number, sometimes following up with handwritten thank-you notes.

“We put a lot of work into making these people feel like we would represent all of Berkeley, not just students,” Sarveshwar said.

The members of Robinson’s entirely student-run operation boasted a combined total of zero years’ professional experience on political campaigns.

“It was really learning as we went,” Sarveshwar said.

It worked. On election day, Robinson claimed 56 percent of the vote and a resounding victory, 22 points ahead of the second-place finisher, Cecilia Rosales. The number of votes counted for Robinson — 1,580 — exceeds the total number cast four years ago in the race for District Seven.

Robinson’s candidacy also earned the approval of an arguably tougher set of judges: the current members of the City Council. He secured endorsements from all eight members and Mayor Jesse Arreguín.

“That was a big moment for us,” Robinson said. “This isn’t just a bunch of kids trying to take over the city.”

Worthington called council members’ unanimous backing “incredible. Unprecedented. ...We have three different factions on the City Council. Nobody ... has ever gotten all three factions to endorse them.”

Worthington has been on the council for 22 years, or as long as Robinson has been alive. Eight years ago, he said, he started looking for a UC Berkeley student to replace him.

“I wasn’t just looking for any student,” Worthington said. “There have been many students who have wanted to run over the years, and I didn’t step aside.”

Robinson, however, measured up.

“Seeing how he would get the other senators to vote for his items ... he’s taken on some very difficult projects and accomplished them,” Worthington said.

To Robinson, having been a student the past four years provides an ideal background for navigating the “unique tensions” between students and long-term residents — which he calls his “biggest project” as a council member.

We’re “trying to help residents think more inclusively of one another,” he said.

After a brief, post-campaign “hibernation,” Robinson has begun his transition planning. He has a budget for one full-time staffer, and he plans to hire a UC student.

City Council members are allowed to hold other jobs, but Robinson has no plans to look for one. “I’m really committed to putting every minute that I can into this,” he said.

In his first job out of college, Robinson will earn just over $30,000 a year.

It’s “livable,” he said. “It’s not going to help out with retirement or anything.”

Holly Honderich is a San Francisco Chronicle staff writer. Email: holly.honderich@sfchronicle.com Twitter: @hollyhonderich