Roscoe, who ascended through the ranks over more than two decades at the Salem museum, will step down from her role at PEM at the end of June. Kurt Steinberg, the museum’s chief operating officer and director of collection services, will serve as acting executive director starting July 1. The museums board of trustees will launch a search for her permanent successor in the coming months.

Hartigan, meanwhile, will start on September 8 at SAAM, one of 21 museums in the Smithsonian Institution’s sprawling cultural complex.

“Lynda is a visionary leader whose career reflects a deep commitment to American art, thoughtful scholarship and public engagement,” Lonnie G. Bunch III, secretary of the Smithsonian Institution, said in a statement. “Having begun her career at the Smithsonian, she returns with deep curatorial knowledge and substantial experience that will guide the museum in the years ahead.”

Hartigan, who served as chief curator at SAAM before arriving at the Salem museum in 2003, said it was poignant to leave the museum where she’s spent the bulk of her career for the museum where she got her start.

“When I started as director at PEM, my message was that I’m coming to lead the museum forward,” she said. “That is my message in relation to physically returning to Washington and SAAM: I’m coming to lead this marvelous museum forward.”

Hartigan, who first served as chief curator at PEM, was appointed deputy director in 2016, and, following a brief stint at the Royal Ontario Museum in Toronto, returned to lead the museum in 2021.

Over more than two decades, she played a pivotal role in many aspects of the Salem museum. An expert in the work of Joseph Cornell, Hartigan oversaw interpretation and re-installation of the museum’s new wing. She guided the museum’s exhibition program, and launched new collecting and programmatic areas, including photography, American art, contemporary art, and fashion.

“Lynda has been an inspiring change agent whose ability to gather people around art, experiences, and multidisciplinary ideas has expanded PEM’s leadership in creativity, innovation, and the visitor experience,” Jennifer Borggaard, chair of PEM’s board of trustees, said in a statement. “We will miss her greatly, and are proud that she will now bring her visionary energy to SAAM and the Smithsonian, our country’s national cultural complex.”

Hartigan, who will take over at SAAM from acting director Jane Carpenter-Rock, arrives at a complicated moment for the Washington museum. SAAM’s previous director, Stephanie Stebich, was removed from the role in 2024 amid staff complaints about her leadership style.

The Trump administration has also pressured the Smithsonian to present a more sanitized version of American history, accusing it in an executive order of promoting “narratives that portray American and Western values as inherently harmful and oppressive.”

In roughly a year, directors at three Smithsonian museums have announced their departures, including the National Museum of African American History and Culture, the National Portrait Gallery, and the Hirshhorn Museum and Sculpture Garden.

Nevertheless, SAAM houses one of the world’s outstanding collections of American art, with particular strengths in New Deal-era work, contemporary craft, and American impressionism.

“The fact of the matter is that the art and the craft that has been created, and the visual culture of Americans, is something that people can really turn to for inspiration, hope, and insight,” she said. “The integrity with which that has been at the core mission of the Smithsonian, and, by extension, the Smithsonian American Art Museum, is something that I really look forward to upholding.”

Malcolm Gay can be reached at malcolm.gay@globe.com.