Ablow was born and raised in Marblehead, Massachusetts. He graduated from Brown University in 1983. He did his psychiatry residency at Tufts-New England Medical Center hospitals and in 1987 received his Doctor of Medicine degree from Johns Hopkins Medical School.
While a medical student, he worked as a reporter for Newsweek and a freelancer for the Washington Post and Baltimore Sun. After his residency, Ablow served as medical director of the Tri-City Mental Health Centers and then went on to become medical director of Heritage Health Systems.
Since 1996 Ablow has had a private practice of forensic, adult and adolescent psychiatry with offices in Newburyport, Massachusetts and New York City. Ablow has testified in numerous high-profile cases, including those of Dr. Richard Sharpe, Clark Rockefeller, Richard Rosenthal, Mary Winkler and Joseph Druce.
As a medical student, Ablow became medical editor and producer for Lifetime Medical Television in New York and Los Angeles from 1985-1989. He authored his first book, Medical School: Getting In, Staying In, Staying Human in 1987. In 2003 he created and was the Executive Producer of the CBS Pilot, Expert Witness, starring Matthew Modine.
He has appeared on The Oprah Winfrey Show, the Today Show,The Howard Stern Show, Good Morning America, The Tyra Banks Show, Nancy Grace program),Catherine Crier Live and The O'Reilly Factor.
From June 2006 through September 2007, Ablow was host and executive producer of his own national daily talk show, The Dr. Keith Ablow Show, syndicated by Warner Bros.. On October 17, 2006 he obtained an exclusive interview with John Mark Karr, the man who falsely confessed to being the murderer of beauty pageant child star JonBenet Ramsey. After which, Ablow asserted he was dealing with a "textbook case of pedophilia" and that Karr would continue to pose a threat to society once free.
Following his show's cancellation, Ablow has been a contributing editor for Good Housekeeping Magazine and Men's Fitness, and a columnist for the New York Post. He is also a contributor and blogger for the Fox News Channel.
On January 6, 2010, Ablow was physically assaulted and kicked in the head by white-supremacist and alleged murderer Keith Luke while visiting him in jail. Luke's defense attorneys had hired Ablow to assist with an insanity defense.