[11] Also in 2009, he successfully sponsored legislation with his colleague, Senator James N. Robey, to eliminate the inheritance tax paid by domestic partners on jointly-owned primary residences.

[12] In 2014 he successfully sponsored a bill to make discrimination against transgender people illegal in housing, employment, and public accommodations.

[15][16] In 2007, Madaleno sponsored legislation to increase the value of the Maryland Refundable Earned Income Tax Credit, an anti-poverty tool.

[citation needed] In addition, he helped close a tax loophole that was costing Maryland roughly $10 million a year by passing legislation that stops a common business practice of artificially lowering taxable profits by paying rent, a deductible business expense, to shell companies controlled by the same parent company.

Madaleno authored the Hunger-Free Schools Act of 2017; as a result, qualified students across Maryland now receive free breakfast and lunch.

[7] Madaleno co-sponsored the law implementing the Affordable Care Act in Maryland; a 2017 law against price gouging by generic drug manufacturers; the Firearms Safety Act of 2013, which bans assault weapons and high-capacity magazines; a number of environmental regulations, including a ban on fracking; and legislation to improve public transit.

[19][23] In 2017, Madaleno worked with Maryland's congressional delegation to restore federal funding for programs that protect the Chesapeake Bay.

[27] In November 2018, it was announced that Madaleno would be nominated to serve as budget director for Montgomery County Executive Marc Elrich.

[1] Along with Delegates Maggie McIntosh, Anne Kaiser, Heather Mizeur, Peter Murphy, Mary Washington, Bonnie Cullison, Luke Clippinger and Meagan Simonaire he formed part of the nine-strong gay grouping in the Maryland General Assembly.

[31] Madaleno is a member of Cedar Lane Unitarian Universalist Church, where he has chaired the Social Justice Council and taught Sunday School.