In 1978, he joined Booz Allen Hamilton in New York to work on U.S. Military Defense Command and Control Systems, requiring security clearances from the U.S. government.

[2] In 1981, he joined Chase Manhattan Bank, leading a team charged with building the organization's international data and money transfer network.

[2] In 1989, Maragos founded his own business, SDS Financial Technologies, and was its president and CEO for over 20 years until his election as Nassau County Comptroller in 2009.

Maragos proposed that Nassau County should become a place where people would "want to come to receive the best medical treatments and where the next generation of miracle medicines would be discovered".

He urged greater focused investments in innovation, research and development, transportation infrastructure and IT to achieve this economic vision.

On October 24, 2016, the Nassau County Comptroller's Office commenced a formal audit of the Town of Hempstead IDA regarding the PILOT granted to the Green Acres Mall.

[7] Maragos conducted and released an audit of a county contract totaling $385,478 in order to monitor the removal of debris caused by Superstorm Sandy.

According to the audit, GEB failed to provide proof that all of its field monitors had the proper FEMA protocol training which was a minimum requirement stated in the contract.

The report recommended that the best option for Nassau County was to negotiate with the MTA to continue with the current service, with a more equitable subsidy.

However, if negotiations failed and Nassau County was forced to contribute the full subsidy demanded by the MTA of over $36 million for 2011, then Maragos ultimately recommended that privatization should be pursued.

The audit, conducted from January 1, 2013, to December 31, 2015, revealed that poor internal controls led to a loss of $2.9 million in county revenue.

Missed violations from a lack of Item Pricing Waiver inspections resulted in approximately $1.5 million in uncollected fees.

[14] Other honors and awards include: Maragos announced on September 29, 2016, that he would seek the Democratic nomination for Nassau County Executive in 2017.

Brian Nevin, the spokesman for Republican Edward P. Mangano, called him an opportunist with Conservative values that he trumpeted during his two failed Senate campaigns.