Born October 6, 1999, in Los Angeles, California, Deommodore Lenoir attended Salesian High School in Los Angeles before playing college football for the University of Oregon Ducks. On September 9, 2020, Lenoir announced his decision to forgo his senior season and declared himself eligible for the 2021 NFL Draft. He received an invitation to play in the 2021 East-West Shrine Bowl before it was cancelled due to COVID-19. NFL.com lead analyst Lance Zierlein projected Lenoir as a sixth or seventh-round pick, while Bleacher Report ranked him as the fifteenth-best cornerback prospect and projected him as a fourth-round selection.

The San Francisco 49ers selected Lenoir in the fifth round with the 172nd overall pick in the 2021 NFL Draft, making him the second cornerback drafted by the team and the twenty-fifth cornerback selected overall. He signed a four-year, $3.76 million rookie contract. Strengths include exceptional instincts and ball skills demonstrated by his eight career interceptions, physical tackling ability at 200 pounds despite standing just five feet ten inches tall, outstanding versatility allowing him to excel in both man and zone coverage, and impressive durability evidenced by starting sixty-four of seventy-nine career games.

During the 2022 playoffs, Lenoir emerged as a postseason star, recording interceptions in back-to-back playoff games against the Seattle Seahawks in the Wild Card Round and the Dallas Cowboys in the Divisional Round, helping propel San Francisco deep into the playoffs. On October 6, 2024, against the Arizona Cardinals, Lenoir returned a blocked field goal sixty-one yards for his first career touchdown in a dramatic 24-23 loss. In the 2025 divisional round against Seattle, Lenoir's dominant performance against Seahawks star wide receiver Jaxon Smith-Njigba became legendary—over fifty-nine coverage snaps, he allowed just one reception for two yards, completely neutralizing one of the league's premier receivers.

On November 12, 2024, the 49ers rewarded Lenoir's excellence with a five-year, $88.88 million contract extension including $38.35 million guaranteed. Through the 2025 season, Lenoir has accumulated 326 combined tackles, eight interceptions, and thirty-one pass deflections across seventy-nine regular-season games. His 2025 snap count of 1,065 ranked third among all NFL cornerbacks, while his Pro Football Focus coverage grade of 66.6 placed him forty-third among 114 qualifying cornerbacks, demonstrating his elite workhorse status and consistent performance.