Geist has hosted the Macy's 4th of July Fireworks and Rockefeller Center Christmas Tree Lighting on NBC.

[6] Geist attended George Washington Middle School in Ridgewood, New Jersey, where he met his future wife, Christina Sharkey.

Geist graduated cum laude from Vanderbilt University in 1997 with a Bachelor of Arts in political science and French.

[7] Geist began substituting as a co-host on MSNBC's 6–9 a.m. morning time slot almost immediately after Don Imus was fired in late April 2007.

[10] Geist and Sunday TODAY earned the prestigious Edward R. Murrow Award for similar coverage on August 4, 2019, the morning after mass shootings in El Paso, Texas and Dayton, Ohio.

He is a frequent guest on Andy Cohen's late night Bravo show "Watch What Happens Live", where he often is paired with a Real Housewife.

Saturday Night Live cast member Mikey Day impersonates Geist during SNL's sketches about Morning Joe.

In 2019, Geist participated with Jenna Bush Hager in a special episode of How Low Will You Go that aired on the Today Show.

Geist also is a board member at Operation Mend, an organization at UCLA Medical Center that provides free surgery and care to America's most severely injured military veterans.