The contract includes a club option for a fifth season and is pending a physical. The deal is expected to be in the $72-78 million range.
Shields spent the last two seasons pitching in Kansas City, where he was the No. 1 starter for last year's American League champions. He finished last season at 14-8 with a 3.21 ERA and a league-leading 34 starts. He rejected a one-year, $15.3 million qualifying offer in the offseason.
Shields' arrival is an unlikely union with Myers, as the two were the centerpieces of a blockbuster 2012 trade that sent Myers to Tampa Bay and Shields to Kansas City. A native of Newhall, Calif., Shields is also returning to his home state.
The 33-year old starter has made at least 20 starts in all nine of his big league seasons and has started at least 30 games in eight of them. His arrival in San Diego will be the first time he's ever pitched for a National League team after spending his first nine seasons between Tampa Bay and Kansas City. Shields has a 114-90 career record with a 3.72 ERA.
- Gabriel Baumgaertner and Scooby Axson