Maj. Gen. William Reddel, the Guard's adjutant general, said the decision was based on new guidance from the Pentagon regarding the Pay Our Military Act.
"It's vital to the good order of our state and nation to have our uniformed men and women back to work as soon as possible," he said. "This is good news for our troops and their families, and a direct result of the hard work of New Hampshire's congressional delegation and governor."
Last week, about 120 guard members came back to work after the shutdown that began Oct. 1 when Congress failed to agree on a spending plan. Many of the 309 members recalled to work Monday are technicians that provide services including health care and family support, repair and maintenance, training, supply and human resources.
About 30 guard members remain furloughed, and Reddel said training and readiness will be harmed if the shutdown continues.
"We are still operating in a very unstable environment," Reddel said.
Meanwhile, many of the 1,200 furloughed workers at the Portsmouth Naval Shipyard also were returning to work Monday.
A shipyard spokesman said workers who are part of the Naval Sea System Command, the Naval Facilities Engineering Command and base support returned Monday morning. Other workers were being told to contact their supervisors to see if they'll be working.