The attack happened in the Preston Road area sometime between 23:00 and midnight on Thursday.
The victim was punched and kicked by the three men as he approached the railway bridge, resulting in a broken wrist.
The suspects were described as being white and in their 20s. They had a brown staffie-type dog with them.
Police have urged anyone with information to contact them.
Det Con Ally Urquhart, from Livingston CID, said: "The victim suffered a painful hand injury during this assault and we're in the process of trying to establish the full circumstances surrounding this incident.
"Anyone who was in the Preston Road area late on Thursday evening and saw anything suspicious is asked to contact police immediately."
A 39-year-old man was attacked by three others as he walked along a road in Linlithgow.