The facility in the state of Georgia is regarded as symbolising close partnerships between the two countries in the electric vehicle (EV) battery sector.
The company is investing around $2.6 billion in the construction project, with trial production under way starting in March.
"This plant symbolises friendship and high-tech cooperation between South Korea and the United States," Moon said in a speech on Saturday.
"South Korean firms are best partners in the battery field. Cooperation in the sector offers a good opportunity for the U.S. and South Korea to develop together," he added.
The Joe Biden administration is pushing to secure stable supply chains in such high-tech industries as semiconductors and EV batteries.
Moon said he and Biden had discussions on promoting mutual investments and joint technology development, reports Yonhap news agency.
He added South Korean businesses are working closely with the US in the chipmaking and future car sectors as well.
SK is partnering with Ford Motor for a joint venture to manufacture EV battery cells.
Once its construction is completed on the outskirts of Atlanta, the facility is expected to become a "successful cooperation model" between the two nations, according to Moon's office Cheong Wa Dae.