During his tenure in the Legislature, Isenberg served as Chair of the Assembly Judiciary Committee (1989–96) and Assistant Speaker pro Tempore (1986–88).
He served on the following standing Assembly committees: Health (1982–94), Water, Parks & Wildlife (1982–93), Judiciary (1986–96), Revenue & Taxation (1987–94), Rules (1984–88), Ways and Means (1986–88), Housing & Community Development (1995–96), Elections, Reapportionment & Constitutional Amendments (1988–90), Consumer Protection, Governmental Efficiency & Economic Development (1995–96), Banking & Finance (1995–96), Public Safety (1994) and Utilities & Commerce (1996).
In 1998, Isenberg was one of three individuals selected by Governor-elect Gray Davis to help prepare his 1999-2000 budget.
Isenberg served as the vice-president of WEAVE (Women Escaping a Violent Environment) which is located in Sacramento.
In 2004, Isenberg became the chair of the Marine Life Protection Act Blue Ribbon Task Force, which is conducting a two-year study of how best to protect the oceans off California.