Robertson agreed to a four-year deal worth $46 million.
In the trade, the White Sox will get Samardzija and pitcher Michael Ynoa. The A's received infielder Marcus Semien, right-hander Chris Bassitt, catcher Josh Phegley and minor league infielder Rangel Ravelo.
Yahoo! Sports' Jeff Passan was the first to report the trade for Samardzija.
Samardzija was traded to Oakland from the Chicago Cubs last summer and went a combined 7-13 with a 2.99 ERA in 33 starts for the two teams.
Robertson went 4-5 with 39 saves in 44 chances with a 3.08 ERA as the main closer for the New York Yankees last season. He turned down the Yankees' one-year qualifying offer worth $15.3 million after reportedly seeking Jonathan “Papelbon money” in free agency.
The Philadelphia Phillies signed Papelbon to a four-year, $50 million deal in 2011, making him the highest-paid reliever ever. The Yankees will receive an extra draft pick in June’s draft as compensation for Robertson signing with another team.
Robertson immediately boosts the White Sox bullpen, which was one of the worst in baseball last season. The bullpen, which only had 36 saves last year, had a combined ERA of 4.28, ranking 28th out of 30 MLB teams.
- Scooby Axson and Sarah Barshop