Holcomb was nominated to fill the remainder of Lieutenant Governor Sue Ellspermann's term after she resigned on March 2, 2016, to become president of Ivy Tech Community College.

Holcomb served in the United States Navy for six years, first at Naval Station Great Lakes and later in Florida and Portugal.

They faced 2012 Democratic nominee and former Indiana House Speaker John R. Gregg and his running mate, State Representative Christina Hale.

Additionally, early in his first term, Holcomb pardoned Keith Cooper, who served eight years in prison after being wrongfully convicted of an armed robbery; declared a disaster emergency at the East Chicago Superfund Site; and ended contract discussions between the Indiana Finance Authority and Agile Networks to manage Indiana's communications infrastructure, including cell towers.

[26] In April 2017, the Indiana legislature approved Holcomb's request for higher fuel taxes and BMV registration fees to fund infrastructure spending, primarily on road maintenance and construction.

[31] Regardless of whether Holcomb was directly involved, OSHA eventually dropped the citations against Amazon's fulfillment center and the case was reclassified as one of "employee misconduct" rather than a shortfall in training and safety procedures.

[30] In July 2020, Attorney General Curtis Hill accused Holcomb of overstepping his authority by issuing a statewide face mask mandate with criminal penalties.

Chief Justice Loretta Rush wrote in the unanimous opinion, "Simply put, absent a constitutional amendment ... the General Assembly cannot do what HEA-1123 permits, ... our Constitution authorizes only the Governor to call a special session, the General Assembly can set additional sessions—but only by fixing their length and frequency in a law passed during a legislative session and presented to the Governor.

1041, a bill passed by the Indiana General Assembly that would prohibit transgender women from participating in state-sanctioned girls' sports.

He cited the bill's low probability of surviving judicial scrutiny and the lack of pressing concern as his reasons for vetoing it.

[35] In the spring of 2023, Holcomb signed several LGBTQ+-related bills into law, including one that bans gender-affirming care for transgender minors,[36] one that requires that parents be immediately notified if a transgender student comes out to a teacher and prohibits discussions of "human sexuality" up to grade 3,[37] and one that bans gender-affirming surgery for inmates in Indiana Department of Corrections facilities.

[38] Holcomb called a special session shortly before the Supreme Court of the United States overturned Roe v. Wade in order to address tax rebates amid the early 2020s inflation surge.

After Roe was overturned, the Indiana General Assembly passed a near-total ban on abortion procedures, allowing exceptions only in the case of rape up to 10 weeks into pregnancy and threat to the mother's life.

On December 18, 2024, convicted mass killer Joseph Edward Corcoran became the first death row inmate to be executed in Indiana since 2009.