"We are very pleased to come to a quick agreement with Dave and also delighted to have pinch hitting specialist Mark Sweeney back in a Padre uniform, where he was an integral part of the 1998 Championship team," said Towers.
Roberts, acquired in a trade on Monday, signed a one-year deal to avoid arbitration.
He appeared in a combined 113 games with the Los Angeles Dodgers and the Boston Red Sox in 2004, batting .254 (81-for-319) with seven triples, 14 doubles, 35 RBI and 38 stolen bases in 41 attempts.
Sweeney, 35, will be returning for his third tour with the Padres, signing a one-year deal.
The left-handed hitting Sweeney had his most productive offensive season with the Colorado Rockies in 2004, and one of the best by a pinch hitter in recent history, batting .266 (47-for-177) with nine homers and 40 RBI in 122 games. He led all Major Leaguers with 23 pinch-hit RBI, the most by any player since 1988, while also hitting five pinch-hit home runs, the fourth highest total ever. In addition, he established new career-highs in hits, doubles (12), home runs and RBI and tied his career-high in games played, while batting .556 vs. left-handed pitchers.