It is the largest private heritage organization in Washington state, maintaining a collection of nearly four million artifacts, photographs, and archival materials primarily focusing on Seattle and the greater Puget Sound region.

A portion of this collection (roughly 2% at any given time) is on display in the museum's galleries at the historic Naval Reserve Armory in Lake Union Park.

In addition to both permanent and temporary exhibits, MOHAI administers ongoing youth and adult programming, and regularly hosts public events in partnership with other community organizations, particularly within the South Lake Union neighborhood.

[2] In 1911, Morgan and Emily Carkeek hosted the first annual Founder's Day party at their home, which was an invitation-only event where guests dressed in historic costumes and brought artifacts and documents related to early Seattle.

[3] The impending reconstruction of State Route 520 and the Evergreen Point Floating Bridge forced MOHAI to move from the Montlake site.

Through a $90 million capital campaign, MOHAI did a full historic restoration of the facility, uncovering both the original ceiling and floor and conducting massive safety, accessibility, and systems upgrades.

The exhibit winds through a series of 22 different sections that each focus on a distinct event or era in Seattle history ranging from pre-Pioneer settlements up to the modern day.

[5] Along with numerous artifacts and photographs, the exhibit incorporates a significant amount of interactive media that allow visitors to touch screens or play games that explore different parts of Seattle history and culture.

The space was originally designed as a replica of a ship's bridge in order to train naval recruits during World War II and features a set of south facing windows overlooking Lake Union.

One of the most popular artifacts in the gallery is a working World War II-era TANG periscope from a naval submarine which offers a 360-degree view of Lake Union and downtown Seattle.