In Nellie Stone Johnson’s long and illustrious life, she helped found the DFL party, mentored Hubert Humphrey, accompanied Walter Mondale to Africa and became the first African-American elected to public office in Minneapolis. She helped to desegregate U.S. Armed Forces and fought for education through the Minnesota state college system.

However, you will see not one of those accomplishments depicted in “Nellie,” a new play about the labor and civil-rights activist that opened Saturday at History Theatre. Playwright Kim Hines portrays Nellie’s early life as a farm child and takes her only up to the successful union organizing drive at the Minneapolis Athletic Club in the late 1930s.

Hines has written two ­Nellie characters — one who has passed to the great beyond and is reflecting on her life, and the other a young woman. Regret animates the older woman at the play’s outset. She wants to re-examine this period of her life and question some of the actions she took.

Portrayed with impeccable grace and wisdom by Greta Oglesby, older Nellie weaves through the action that plays out on Michael Hoover’s spare and functional set. Hoover has created opaque panels, which, with Michael Wangen’s lights, allow director Richard Thompson to cast key scenes in shadow.

Oglesby’s character advises her younger self and tempers the impatience of youth. She also serves as a friendly narrator for what can at times seem a pageant.

Shá Cage shows off an inexhaustible reserve of energy, expressing the spirit of young Nellie. Cage never settles for self pity in her portrait of a woman who endured life’s slings and arrows with a fierce work ethic and an ardor for justice.

The other standout in director Thompson’s cast is Ron Collier, who plays Johnson’s first husband, Clyde Stone, and a passionate black minister who urges his community to shun labor unions. James Craven is finely restrained and proper as a protective co-worker of Nellie, and Charles Fraser makes his mark as Swan Assarson, the Swedish immigrant who inculcated Nellie with progressive politics.

Thompson’s staging is brisk and articulate, taking whatever the script gives him.

That, however, gets us back to Hines’ truncated story. A case can be made for a drama that focuses on one aspect of a life that is otherwise too big for a two-hour play. The narrator might frame a period as the defining moment that propelled the heroine to decades of renown. Here, older Nellie’s reflection is that it is “time to move on,” her restless soul now satisfied that you can’t change what is done.

Positively, Hines looks at Nellie’s private life with Clyde, a side of her we rarely see. But Nellie Stone Johnson was not chosen as the subject of a play because of her domestic drama. Several static and talky scenes offer few hints of the greater purpose she felt — a drive that took her to state and national platforms. How did she get there?

Nellie deserves a sharper examination and a clearer sense of her remarkable career.