The Cubs have agreed to a contract extension with Castro that will run seven years in the range of $65 million.
The deal also will include a club option for an additional year. His salary could rise to $80 million if the option is exercised and escalators are met.
''I want to be here for a long time and winning,'' Castro said. ''My family (will) change, but nothing (will) change for myself. (The money is) not going to stop me from working hard every day on the field.''
Castro, a two-time All-Star at 22, entered Saturday's play batting .276 with a .728 OPS, 12 home runs and 58 RBI.
His deal will cover all four years of arbitration, plus two or three free agent years.
''Only the most talented players get to the big leagues at 20,'' said Cubs general manger Jed Hoyer. ''I'm sitting here with a 22-year-old veteran right now. That was a big part of our decision.
''The way it was looking, Starlin was going to be a free agent way too early. He's a big part of our future. We have four years of control with him after this year. By doing this deal, we now have eight.''
Castro, as a Super Two player, qualified for an extra year of arbitration.
News of talks between the Cubs and Castro was first reported by CSNChicago.com.