Daniel Pressland denies stealing and selling works by Alan Davie.
St Albans Crown Court heard he had helped the Scottish artist when he was "confused" and was given two paintings worth £12,000 as a "thank you".
Mr Pressland said he "had no idea" how much the paintings were worth.
He said in early 2014, he arrived at Mr Davie's house in Hertford and the 93-year-old was "just in his underpants and looking confused".
He said he helped the painter, whose works were shown at the Tate Gallery, back into his home and helped him "tidy up."
Mr Pressland said he returned to the house some five weeks later to clean the windows and on this occasion Mr Davie asked him inside.
"He said 'This is for you.' I appreciate what you did and I would appreciate if we could keep it between ourselves," Mr Pressland said.
"He gave me the paintings, 'Toothbrush' and 'Message Sticks.'"
He said he had no idea what they were worth and he took them away in his van that day.
The two paintings were sold at auction for £12,000.
Tyrone Belger, defending, asked him: "As far as you know did Alan have the right to give away his own paintings?"
Mr Pressland said: "Yes."
The 42-year-old, of Outward Common in Billericay, Essex, is accused of stealing 31 paintings.
He has admitted one count of burglary, but denies two further offences of burglary, two of converting criminal property and two of transferring criminal property.
Co-defendant Gavin Challis, 42, of North Street, Nazeing, Essex, has denied possessing criminal property after two paintings by Mr Davie were found at his home.
The trial continues.
A window cleaner, accused of stealing £500,000 worth of paintings from an artist's home, has told a jury he was given artworks by the painter.