"We can neither tolerate nor afford a Legislature that fails to see the big picture," he said.
Gatto's former employer, Rep. Brad Sherman (D-Sherman Oaks) officiated the ceremony, as he did at Gatto's wedding. Joining the two on stage were Gatto's wife, Danielle, and 15-week-old daughter, Eliana Vivienne.
Gatto, who at 35 is the second-youngest lawmaker in Sacramento, thanked supporters and described his first weeks at the Capitol, including being mistaken for a staff assistant more than once.
He took office too late in the legislative year to sponsor bills of his own, but Gatto said he has cast the "deciding vote" in the Assembly on three pieces of legislation. One limits transfers of water rights from agricultural to municipal users. Another bill limits the private information social media websites can post about teens. The third law bans baby bottles made with bisphenol A, which regulators say could be linked to autism and cancer.
The June special election was for a six-month stint to finish the term of Paul Krekorian, who won a seat on the Los Angeles City Council. Gatto will be on the November ballot seeking a full two-year term.
Republican Sunder Ramani, who in June lost to Gatto, 59% to 41%, also will be on the November ballot. Ramani has not said whether he will actively campaign for the seat.
Among Gatto's guests Monday were Rep. Adam Schiff (D-Burbank), state Sen. Carol Liu (D-Glendale), Burbank Mayor Anja Reinke, and Glendale City Councilman Frank Quintero.
FOR THE RECORD: This corrects an earlier version that identified Frank Quintero as Glendale mayor. The age for Mike Gatto's daughter was also incorrect.