Ryu was born in Seoul, South Korea, in 1975, the oldest of three children His father, Eul Chul Ryu, and mother, Michelle Won Chung Ryu, moved the family to Los Angeles, California in 1980, when Ryu was 5 years old.There, Ryu’s father served as editor in chief of the Korean Street Journal newspaper based in Los Angeles, and his mother worked as a nurse. Ryu’s parents were married for over 40 years before his father’s death in 2016.
Ryu later served as Director of Development and Public Affairs for Kedren Acute Psychiatric Hospital and Community Health Center.
Ryu was one of over a dozen candidates to replace Councilmemebr Tom LaBonge, who was term-limited. Ryu and Carolyn Ramsay, a former aide to LaBonge advanced past Joan Pelico, Teddy Davis, Step Jones, Rostom “Ross” Sarkissian, Mike Schaefer, Wally Knox, Tomas O’Grady, Jay Beeber, Tara Bannister, Sheila Irani, Fred Mariscal and Steve Veres, in the March 2015 primary.
Document retention was the first part of Ryu’s agenda to be acted upon. One of Ryu’s first legislative actions in City Council was introducing a motion to require outgoing City Council members to retain documents when an office transitions. The motion passed in September 2016.  Before this motion, there was no rule barring outgoing City Councilmembers from destroying documents before leaving office. . Also soon after entering office, Ryu pushed for a ban on political donations from non-individuals, including corporations, developers, unions, and business groups. No other member of City Council would second the motion, and it did not proceed . In January 2017, Ryu, along with Councilmembers Joe Buscaino and Paul Krekorian, introduced a motion to ban contributions to city elected officials and candidates for city office from developers and their principals with development projects currently or recently before the city as well as increase the matching fund rates from the current 2:1 match in primary elections and 4:1 match in general elections to 6:1 in both primary elections and general elections for all candidates who qualify for matching funds. As of January 2018, the motion was pending in committee .
Preserving residential neighborhoods was another part of the agenda of Ryu. Out-of-scale homes, also known as “McMansions” were a concern to many residents, particularly in Beverly Grove, Hancock La Brea, and the San Fernando Valley. In December 2016, Councilmember David Ryu introduced a “Baseline Mansionizatin Ordinance” to address this city-wide issue This motion intended to limit the scale of the construction and revise the City’s rules which govern the amount of residential floor area that can be developed on a single-family lot through the approval of the Baseline Mansionization Ordinance (BMO) and Baseline Hillside Ordinance (BHO). The ordinances were passed and went into effect in March 2017. Councilmember Ryu expanded the Historic Preservation Overlay Zone to include the Miracle Mile neighborhood on Wilshire Boulevard in Los Angeles. This zone preserves the unique and historic character of a neighborhood while still allowing for new housing opportunities .
Ryu became the first city councilmember in Los Angeles to appoint a panel of citizens to oversee and advise how he uses his discretionary funds, dubbed “The Discretionary Funds Task Force”. In Los Angeles, each one of the 15 members of City Council are apportioned “discretionary funds” from the city’s budget to be used on projects in their district. However, disclosure of how this money is used is not required, and there is little oversight . To address this, Ryu introduced his Discretionary Funds Task Force, which doesn’t have the authority to tell the Councilmember how to spend his discretionary funding, but can make recommendations and advise the Councilmember on how to use this funding. Councilmember Ryu also became the first and only councilmember in Los Angeles to make his discretionary spending history publicly available on his website