San Buenaventura first entered the Hawaii political scene when she ran for the District 4 Democratic nomination for the
Hawaii House of Representatives. The Democratic primary was a crowded one that included four challengers, including San Buenaventura, and incumbent representative
Faye Hanohano, who had held the seat since 2006. San Buenaventura emerged as the only challenger to top Hanohano, and won the primary carrying 43.4% of the vote. In the general election, she faced Republican nominee Gary Thomas, whom she defeated by 43 points. She assumed office in the House in January 2015. San Buenaventura opted to run for reelection to a second term in 2016, and faced no opposition from fellow Democrats. She advanced automatically to the general election, where she carried 75.5% of the vote against nonpartisan Luana Jones and Constitution Party candidate Moke Stephens. In 2018, San Buenaventura was elected to a third term in the House after she won the primary with no opposition and was later declared the winner of the race after the general election was cancelled. San Buenaventura was Majority Whip, Chair of the House Human Services and Homelessness Committee, and vice-chair of the House Judiciary Committee. In May 2020, San Buenaventura announced that she would run for the District 2 seat in the
Hawaii Senate, which was being vacated by outgoing Senator
Russell Ruderman. She defeated Democratic challenger Smiley Burrows in the August 8 primary, carrying 78.7% of the vote, and advanced to the general election in November to face
Aloha ʻĀina Party candidate Ron Ka-Ipo. In March 2025, as Chair of the Committee on Human Services, Senator Buenaventura stopped a popular bill, House Bill 729, that sought to ban child marriage in Hawai'i. The bill would have raised the legal age of marriage from up from 15 to 18 years old. "In a statement, the senator said marriage can provide benefits to youth who are trying to escape an abusive family situation, are pregnant or want to get on their partner’s health insurance. “I am always leery of national advocacy groups who just want to notch Hawaiʻi as a win without taking into account the culture and circumstances here,” San Buenaventura said." ==Electoral history==