The 27-year-old returns to the National League North a year after earning promotion from it.
He helped take Harrogate up in 2018, the attacker scoring 16 times.
New manager Craig Elliott hopes he can repeat the trick for the Pilgrims when the season gets going.
He told the club’s website: "Dominic is a player who had teams in the league above keen to sign him, so it is a great coup for the club.
"He is a calm and clinical finisher and he can play both the number 9 and number 10 roles, so this signing gives us good options
"He knows the league, a large majority of the players already signed and is hungry to get another promotion on his CV, so I am delighted to bring Dominic to Boston United and be able to work with him next season."