The IGIS has oversight over the Government Communications Security Bureau (GCSB) and the New Zealand Security Intelligence Service (NZSIS).
Although she said a lot needs to remain secret in order for the agencies to be effective – that does not create a "blanket of secrecy" extending to all aspects of their work.
Gwyn said the IGIS had been transparent in a number of ways.
"I have published two inquiry reports and have completed five reviews, and initiated several more," she said.
These include IGIS' report on how the GCSB undertook intelligence activity in relation to New Zealand's interests in the South Pacific.
IGIS also conducted a review of the New Zealand Classification System.
"For each report, I work with the Director-General of the relevant agency to try to provide as much information as possible publicly without compromising national security," Gwyn said.
She added that two more reviews are set to be published before the end of the calendar year.
Between the two agencies, there were 26 complaints from members of the public in the 2017/18 year – nine for the GCSB and 17 for NZSIS.
"A substantial proportion of the complaints received in this reporting year were from members of the public who believed that one or both of the agencies had undertaken surveillance against them," the report said.
"Other complainants were concerned that the agencies had used some kind of weapon against them."
In each case, at Gwyn's request, the relevant agency confirmed that it held no information about the people who had complained.
This year, the IGIS reviewed 65 GCSB warrants and 32 NZSIS warrants.
"Overall, I certify that both the New Zealand Security Intelligence Service (NZSIS) and the GCSB each have sound compliance procedures and systems in place."
Looking ahead, Gwyn said she expected both agencies will be able to respond to IGIS' requests for information and clarification, and to the substance of draft reports, "in a more timely manner".