The 48-year-old finished the 560km (348 mile) gruelling swim from Land’s End in Cornwall to Dover in Kent in 49 days.
He was greeted at Shakespeare Beach by Environment Secretary Michael Gove.
The environmental campaigner and UN Patron of the Oceans began the challenge on 12 July, swimming 10 to 20km (six to 12 miles) every day.
Mr Pugh, from Plymouth, Devon, said he felt “relieved and exhilarated”.
“It’s been very, very long, we’ve been going for 49 days and I’m exhausted, physically exhausted, mentally exhausted, so delighted to be here.”
He is estimated to have made 500,000 to 750,000 strokes along the journey.