Boyce’s signing follows the arrival of defender Toby Sibbick on loan from Barnsley on Friday.
Both players could make their debuts when Hearts take on Rangers at Tynecastle on Sunday, live on Sky Sports Football, subject to international clearance.
Boyce scored 14 goals for Burton Albion this season before deciding to switch to the Scottish Premiership side.
The 28-year-old has made 21 appearances for Northern Ireland since 2011, scoring once.
Sky Sports will bring you the very latest news from the January transfer market with the return of three shows.
Start your day with Good Morning Transfers at 9am as our team of reporters bring you the latest news and insight. Transfer Talk then follows at midday delivering analysis of the biggest stories. Then join us at 7pm for the definitive round-up of the day’s news with The Transfer Show.