Sami Rakene, 28, stole a Patek Philippe watch from Edward Barnett in the area of Kilburn High Road, north-west London at about 18:00 BST on 26 October.
The watch’s exact value is unknown, but the luxury brand’s watches can cost between tens of thousands and hundreds of thousands of pounds.
The defendant, of Burnt Oak, Edgware, was also sentenced at Westminster Magistrates’ Court on Tuesday for stealing a white suitcase and a backpack from two different people at Paddington station on 7 April and 1 May respectively.