Gladiolus sekukuniensis is a deciduous perennial with a rootstock that is a corm. The plant is actively growing in summer and flowers in late summer to early autumn (March to April), then goes dormant after flowering is complete. The plant is approximately 0.6–1.1 m tall with long, narrow, grass-like leaves that have a noticeable midrib. The plant produces an erect flower stalk that bears about 8-17 flowers towards the tip. Each flower is white, cream, or pale salmon-pink, often decorated with a thin dark red streak down the center of each petal. Sometimes, the lower petals show a yellow midline, making the flowers look strikingly patterned. The flowers are unscented and have gaps, termed windows, between the upper petals, and narrow, tail-like petal tips that curl or twist. Each flower has a long, narrow tube at its base (perianth tube), 25-35 mm long. If pollinated, the plant produces a dry capsule that contains flat, winged seeds that are easily dispersed by wind.

It closely resembles G. permeabilis subsp edulis in vegetative features and in flower form but differs from it in flower colour and in having a more elongated perianth tube.