The Devils said they had agreed to a one-year, two-way contract with the restricted free agent. The contract is worth $800,000 at the NHL level and $275,000 at the American Hockey League level.
Jaros, 25, split last season between San Jose and its AHL affiliate. He has spent the past four seasons between the NHL and AHL, three with the Ottawa Senators organization. In 83 career NHL games, Jaros has one goal and 13 assists with 35 penalty minutes.
A native of Slovakia, the 6-foot-3, 220-pound Jaros was Ottawa's fifth-round selection, 139th overall, in the 2015 NHL draft.
Merkley split last season between New Jersey and Binghamton of the AHL, finishing with two goals and eight assists in 27 NHL games. Acquired by the Devils in the Taylor Hall trade with the Arizona Coyotes in 2019, Merkley is a former first-round pick who could have some promise for San Jose on a checking line.
The Devils have acquired a surplus of young forwards in Merkley's mold and this move clears up some roster space to perhaps promote one of them during training camp.
Jaros might have a quicker path to a full-time role in New Jersey than he did in San Jose, as he joins a team that lacked defensive depth last season. But the Devils have also added defenseman Ryan Graves from the Colorado Avalanche this offseason, and they could attract another defenseman in free agency, which begins Wednesday.
The Associated Press contributed to this report.