"Tell you what, Chris — I don't want you to die tonight. I need to know what street you're on," Mr Lee told the gravely ill man.
"I want you to get through tonight and chat to me tomorrow, when you haven't got a load of drugs in you.
"I don't want you to die tonight because I love you. I love you, brother. I love you.
"Someone's going to come and help you."
Afterwards, Mr Lee tweeted about the harrowing experience.
"We managed to keep him online, get a description of what he looked like and was wearing, work out where he was and send an ambulance and police to him.
"Kept him on the phone for 30 minutes while he got harder to understand.
"Long periods of silence where I thought he'd died. F**k, that was intense and upsetting.
"I really hope he makes it."
Later, Mr Lee broke down in tears after being told paramedics had reached Chris in time and managed to save him after the show's producer gave emergency services a description of the man and his location.
According to The Sun, a South Western Ambulance Service spokesman confirmed the radio station staff had helped saved the man.
"Paramedics were called at 11pm, December 19 to Derry's Cross, Plymouth by a radio station who were concerned for the welfare of a patient," the spokesman said.
"The male patient was treated at the scene and taken onto Derriford Hospital ED for further treatment."
Mr Lee was also showered in praise by Cornwall Police on Twitter.
"This is a very typical call for us sadly and December is a hard month for many," Inspector Kev Morley said.
"We will do our best to direct him to long term support. And thanks to you for the part you played. We all have a role to play in supporting those that are struggling."
Mr Lee, who appeared on the UK version of I'm a Celebrity in 2017, later thanked his supporters for their kind words on social media, where he has been described as a hero.
"Been an odd day for so many reasons. I really appreciate your kind words," he tweeted.
"Just read about the incident on @iainlee's show last night. He might have thought he was just doing the right thing, but that is hero level stuff. The biggest tipping of my hat possible. You never know when you might have to save your own 'Chris'," one Twitter user wrote, while another added: "I listened to this last night and @iainlee and @FlippinKath did an amazing job. It just shows we all have a role to play in preventing suicide."
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• Samaritans 0800 726 666
• If it is an emergency and you feel like you or someone else is at risk, call 111.
