Duncan Hutchison set off from New York in May on his 3,500-mile journey to Lochinver, north-west Scotland.
He was carrying out the journey in a 23ft wooden rowing boat and has raised more than £18,000 for charity WaterAid.
Mr Hutchison was rescued around 863 miles off the Cornish coast on Saturday by a merchant tanker, which is now taking him back to New York.
A post on his Facebook page said there had been a technical fault on the boat which had left him with no electronics.
It said: “He will be devastated, especially with a technical problem rather than a physical or structural issue of the boat.
“Although he’s totally dedicated to completing the challenge, today marked 100 days at sea, he’s acted responsibly in the best interests of support services, surrounding boats and himself.
“Calling this in was probably the toughest thing Duncan’s ever had to do, but is testament to his selfless and professional approach throughout the journey.”
The Maritime and Coastguard Agency said Mr Hutchison reported that he was in difficulties at around 1am and was “battling two-and-a-half metre waves”.
A spokesman said: “HM Coastguard broadcast alerts to vessels in the area and the man was picked up by a merchant tanker who diverted to the scene.
“His 23ft wooden rowing boat is now being towed by that vessel.”
Duty commander Mark Rodaway said he was “picked up safe and well”.
“We’ll continue to keep in touch with him via the tanker crew while they progress their passage back towards New York,” he added.
“We’re grateful to the tanker for responding and rescuing this rower.”