Avelino grew up in Orange County, the son of immigrant parents who built a successful small business. He attended local public schools from elementary through high school. Avelino earned an associate degree from Fullerton College, a bachelor's degree from San Jose State University, and a master's degree from Johns Hopkins University. After playing Division One college football and briefly pursuing a career in the National Football League, he coached at Fullerton College. He also taught as a special education instructional assistant in the Anaheim Elementary School District.

Avelino served as a Councilmember for the City of Anaheim from 2020-2022. Prior to that, he was the Chair of the City of Anaheim's Budget, Investment, & Technology Commission from 2016-2020. Before that, he worked in the district offices for several elected officials in Los Angeles and Orange Counties.

As a Councilmember, Avelino worked to speed up the rollout of COVID-19 vaccines, expand access to mental health resources, develop new city parks, establish a small business assistance program, and increase accessibility to housing, all while being a responsible fiscal steward of tax dollars. He also worked closely with local police officers, firefighters, and paramedics to make neighborhoods safer and improve emergency response times. On the City of Anaheim's Budget, Investment, and Technology Commission, Avelino focused on economic growth, improving the city's long-term financial stability, and safeguarding public resources on behalf of taxpayers.

Since beginning his term in the State Assembly, Avelino has been appointed Commissioner to the California Debt and Investment Advisory Commission. This Commission evaluates strategies for public debt issuance and investing public funds to reduce the cost of debt and improve credit ratings. Additionally, Avelino was chosen to serve in the Council of State Governments West, in this capacity he participates in informative conversations and collaborates on important state and regional policy efforts.

Recently Avelino was appointed Chair of the Budget Subcommittee on Accountability and Oversight, additionally, he serves on six other committees- Arts, Entertainment, Sports, and Tourism; Budget; Governmental Organization; Insurance; Joint Legislative Audit; and Military and Veterans Affairs. He will listen, work hard, and build the coalitions necessary to reduce homelessness, protect public health, enhance schools, restore lost jobs, decrease crime, combat climate change, expand infrastructure, and improve the quality of life for the residents of the 68th Assembly District. His previous legislative package includes efforts to ensure government accountability, transparency and oversight, and modernizing and streamlining processes.

Avelino is married to his high school sweetheart, Dr. Monica Valencia, who is a local elementary school principal.