Billan had joined the board in April 2019 and will remain a director, while outgoing CEO Nav Dhaliwal was appointed executive chairman.
Billan was a business development analyst from 2012 for Nevsun Resources, which was acquired by Zijin Mining in 2018 for US$1.4 billion.
Dhaliwal said Billan had extensive experience in corporate development and was well-respected.
"His leadership will be a great asset to Gatling - helping to advance the Larder project through its next major phase of growth and unlocking value in the company," he said.
In September, Gatling said it had succeeded in connecting three, high-grade gold deposits at its Larder project.
Billan said Gatling planned to enhance existing shareholder relationships and bring in new shareholders who saw "Gatling's inherent and intriguing value gap".
The company said Peter Damouni had resigned as chairman and would continue to act as a director.
Gatling shares (TSXV: GTR) are trading near the bottom of a one-year range of C23.5-56c.
They closed up 3.8% or 1c to 27c, capitalising it at $12.3 million (US$9.3 million).
