Des Moloney, 28, of Chobham, Surrey, landed in a Sainsbury's car park near Colchester in Essex, but only suffered cuts and bruises.
The pilot, his brother Tom, 31, said last night: 'It's a miracle he is alive. I still can't believe it.'
The incident happened after they took off from North Weald aerodrome. Tom said: 'I had climbed to 3,000ft and was doing 250 miles an hour when I rolled the aircraft. While we were upside down there was a malfunction with the ejector seat and it released him when it shouldn't have done.
'Des went crashing through the glass. He just exploded through it like a rocket. I thought he was a gonner.
'I circled around but it was a nightmare trying to fly the plane without a canopy and I couldn't see any parachutes. It was the worst 15 minutes of my life and I was convinced I had lost my brother.' He then returned the aircraft to the aerodrome.
'I was absolutely amazed when I was told he was alive. He had become separated from his seat but he had a parachute strapped to his back. His ejector seat landed in the garden of a house in nearby Stanway.
'My brother isn't a pilot. He just comes up with me for the fun of it. But he did all the right things. Fortunately he was conscious and he managed to stay cool and pulled the rip cord then floated to the ground,' he said.
'I never want to go through anything like that again. I'm still shaking now.'
The brothers' father, also Tom, 61, of Feltham, Surrey, said: 'Tom rang on his mobile phone as they were on their way to hospital. He told me Des had fallen out of the plane but at that stage they thought his only injury was that he had bitten his tongue. I was horrified.'
A police spokesman said the Civil Aviation Authority would investigate the cause of the ejector-seat malfunction.