Two self-help gurus who emphasised the pursuit of happiness committed suicide together in their New York apartment, police have said.

Motivational speaker John Littig, 48, and his common-law psychotherapist wife, Lynne Rosen, 46, encouraged listeners to embrace spontaneity on their radio show, The Pursuit of Happiness.

One of their in-air mantras was "it's always too early to quit" but detectives believe they had killed themselves as part of a suicide pact.

They were found dead on their couch with plastic bags over their heads and a tube attached to a canister of helium, according to police.

A spokeswoman for medical examiner's office said that autopsies confirmed that both Littig, 47, and Rosen, 45, died from asphyxiation after inhaling the gas.

Lettig had allegedly claimed in a note found at the scene that his wife was in too much pain. In another note, Rosen apologised to her family.

The duo's monthly radio show on WBAI focused on personal development and growth and they founded life-coaching company Why Not Now, which held self-help workshops.

During one broadcast, available on YouTube, Rosen encouraged her fans to fight depression with a positive attitude.

"People get scared to make changes and step outside of that comfort zone, right, John?" she says.

"Stepping outside you comfort zone is very important. Or alternatively you can start to get comfortable with change," he responds.

"Yeah! I like that!" she says. "That's great."

An 87-year-old neighbour paid tribute to the couple, who had reportedly lived in their Brooklyn apartment block for 20 years.

"I knew them for many years. They were always respectable," she said.