[2] He was a Commissioner and Vice Chairman of the New York State Housing Finance Agency from 1978 to 1979.

[2] Marrero is well known for twice striking down elements of the USA PATRIOT Act, most recently in September 2007, stating that the provision in question "offends the fundamental constitutional principles of checks and balances and separation of powers.

"[3][4] On October 7, 2019, Marrero dismissed an attempt by President Donald Trump to prevent his accountants from complying with a New York prosecutor's subpoena for eight years of President Donald Trump's tax returns.

[5][6] On February 11, 2020, Marrero allowed T-Mobile and Sprint to complete their merger after nine states and the District of Columbia sought to block it.

In the ruling, he held that the prosecutor's grand jury subpoena was valid and the Presidents attempts to challenge it were dilatory and without merit.