[2] Founded in 1863 by Father William R. Scott, it was the principal school of the former Anglican Church of Hawaiʻi.

[3] On October 11, 1862, Thomas Nettleship Staley arrived in Hawaiʻi by request of Kamehameha IV and Queen Victoria of the United Kingdom.

Before Staley, too, left the islands for Britain in 1870, Father Mason merged the two schools and relocated it to the St. Alban's campus.

The St. Alban's College, intended for white students, separated and continuing operating at Pauoa until 1887.

ʻIolani School grew and refined its program offerings with a standard college preparatory curriculum as a foundation for every student.

Religion, performing and visual arts, music, and athletics became integral parts of the ʻIolani School education.

[8] Orchestra and Choir also use this building for their Performing Arts classes for both Upper and Lower School students.

The Sullivan Center for Innovation and Leadership was finished at the end of 2012 for the replacement of the Upper School Library.

The Sullivan Center was created to emphasize sustainability and includes classrooms, laboratories, an auditorium, and a garden among other facilities.

[10] The Kaneshiro Science and Innovation Center and the Sidney and Minnie Kosasa Performance Studios and Courtyard were both opened for the 2019 school year.

Since the formation of the Hawaii High School Athletic Association, ʻIolani has won over 75 state championships in various sports.

[18][19] Each year his legacy is honored via the Keables Chair, which brings "outstanding teachers, writers, and artists to ʻIolani.

"[20] The ʻIolani Fair has been held every year in late April to fundraise for student expenditures.

[27] ‘Iolani has won the Hawai’i Regional Science Bowl in the High School division since 2015.

Team members J. Hara, C. Kodama, E. Masutani, M. Muraoka, D. Reiss, T. Van Etten, M. Williams represented the state of Hawaiʻi March 26–29, 2010 at the Smithsonian Air and Space Museum in Washington, D.C., placing second at the national level.

The ʻIolani team (2438a) was part of the winning alliance, and qualified for the 2009 VEX World Robotics Competition, to be held at Dallas, Texas.

At the 2010 VEX World Robotics Competition, they won the notable CREATE award for design, as well as placing as division semifinalists.

In the 2011 VRC season, ʻIolani's VEX team again was in the winning alliance at the Pan Pacific Competition.

ʻIolani School's Gender-Sexuality Alliance strives to promote inclusivity on campus and allow spaces for discussions on contemporary issues such as gender identity, pronouns, and sexuality through student-submitted questions, in addition to ice breakers for members and media with representation LGBTQIA+ individuals.

Originally the 'Iolani School International Affairs Association, or ISIAA, ʻIolani's Model United Nations club has competed in various conferences since its founding in 2011.

With the help of coaching by two advisers and student leadership, the numerous delegates who have joined since the club's founding have competed in a number of conferences, amassing a multitude of awards from different committees.

The chamber music program at ʻIolani School allows for talented students to be coached weekly by virtuosic musicians from around Hawaiʻi.

During the semester, each group practices and prepares a piece to be performed at a recital held in the middle and end of the school year.

These quartets are possible due to the gracious support of sponsors and continue the musical growth and education of ʻIolani students, allowing for the unique experience of playing in chamber ensembles.

The active participation of ʻIolani's surf team in numerous competitions around the island has yielded great achievements to its members.