Horse found in Paddington by poor person (6)
I believe the answer is:
beggar
'poor person' is the definition.
(beggar is a kind of poor person)
'horse found in paddington' is the wordplay.
'horse' becomes 'gg'.
'found in' means one lot of letters goes inside another.
'paddington' becomes 'bear' (I've seen this before).
'gg' put into 'bear' is 'BEGGAR'.
'by' is the link.
(Other definitions for beggar that I've seen before include "Pauper who seeks alms" , "Mendicant or humble supplicant" , "I ask you!" , "Down-and-out" , "poor chap" .)