After more than 20 years in Portland’s Congress Square art district, the Children’s Museum and Theatre of Maine has obtained the approval it needed to leave the city’s downtown.

The Planning Board on Tuesday night unanimously approved a site plan permit that will allow the museum to move into a yet-to-be-constructed building at Thompson’s Point, the site of a burgeoning mixed-used development off outer Congress Street on a peninsula that juts out into the Fore River.

Development plans filed with the city call for construction of a 29,000-square-foot, three-story cultural center on 1.12-acres at Thompson’s Point.

Suzanne Olson, the museum’s executive director, said before the meeting that the organization hopes to occupy the new building by the spring of 2019.

Olson said the building that houses the existing museum at 142 Free St. will be put on the market and sold, but its programs for thousands of Maine children will continue to be offered there until the new building is ready to be occupied.

The new building will include 18 on-site parking spaces for staff and guests and an additional 64 parking spaces that will be designed into a new loop road under construction. The museum will be partnering with Forefront Partners to develop the new facility.

The museum moved into the Free Street building, which once housed the local Chamber of Commerce, in 1993. It is located near the Portland Museum of Art.

The $10.5 million relocation project faced virtually no opposition from the community. No one spoke against the project during Tuesday’s public hearing.

Jim Marcisso, past president of the museum’s board of directors, said the museum has outgrown its Free Street location and has desperately needed more space for several years.

“Our single biggest challenge to our mission has been the building space,” Marcisso told the Planning Board. He said Thompson’s Point will not only serve the museum well, but will offer access to public transportation and outdoor play space that currently does not exist downtown.

“I think the museum is an indispensable tradition here in Portland,” said Michael Bourque, who serves on its board of directors. After museum officials looked at 22 possible locations, Bourque said, Thompson’s Point turned out to be the best site. “This is the place.”

“The Children’s Museum of Maine is a beacon of light for the city of Portland and for the children of Maine,” Joshua Murphy said while urging the Planning Board to approve its site plan.