After winning the general election in November 2015 for a fourth term, McDermott became the longest-serving mayor in Hammond's history.

[8] During McDermott's first term in office, the dilapidated River Park Apartment complex was razed under the guidance of the Hammond Redevelopment Commission.

Critics at the time referred to the generous tax abatement awarded Cabela's as "corporate welfare" while supporters, including the mayor, cited a "public-private partnership.

[13] According to McDermott, this department was an example of duplicate government better left to the county to operate, while mayoral detractors claimed it was a valuable and much-needed service to the city, especially its poorest citizens.

[22] In February 2014, McDermott agreed to the $200,000 settlement of a discrimination complaint filed by Hammond Housing Authority Director Maria Becerra.

[23] An editorial in The Times of Northwest Indiana later called for McDermott to make a public apology in the wake of Becerra's ouster from the Hammond Housing Authority.

[26][27] On May 5, 2015, McDermott became the first mayor in Hammond's history to win four consecutive democratic primaries when he handily beat 6th District Councilman Homero "Chico" Hinojosa with 78% of the vote.

[28] In 2015, complaints were dismissed by the Lake County, Indiana election board that McDermott allegedly violated finance laws for not properly itemizing over $200,000 in reimbursements for food, lodging, and rental cars.

[30] Following Pete Visclosky's decision not to seek reelection to the United States House of Representatives for Indiana's 1st congressional district in the 2020 election, McDermott declared his candidacy for his seat.

[34] On October 16, 2022, McDermott participated in a live televised debate with Incumbent Republican Senator Todd Young, and Libertarian candidate James Sceniak.

[citation needed] On election night November 8, 2022, McDermott conceded his senate campaign to Republican Todd Young.