The 26-year-old was scheduled to appear at the music event last June (15), but was forced to withdraw because of vocal surgery.
"Last year I had to cancel Glastonbury," an emotional Jess told the crowd on Friday (24Jun16). "I don't think I was meant to be standing on this stage last year. Over the past year a lot happened and I'm so grateful."
The flame-haired Brit took to the stage at the festival in an emerald green sequinned suit, and opened her set with her hit Don't Be So Hard On Yourself.
Despite the grey skies at the Worthy Farm venue, she told the crowd, "You all look amazing. I'm here to bring love and happiness because the weather is so awfully s**t."
After her rousing renditions of No Rights, No Wrongs, and Gave Me Something, the sun began to shine through the clouds, and she called her set an "amazing moment".
"Two years go, if someone told me I'd be standing on this stage singing to this many people, I'd have been like, 'Shut up'," Jess gushed. "Standing here right now is one of those amazing moments."
She then slowed down her energetic set with a piano-led version of her hit My Love, and urged the crowd to sing along.
Jess also belted out a powerful rendition of Chaka Khan's classic I Feel For You and closed her set with her number one hit Hold My Hand.
Jess previously revealed she was terrified before the surgery on her vocal chords last year, and told British newspaper The Mirror she was scared she would do more damage to her voice.
"I had a polyp on my larynx and some bleeding, and I completely pooed my pants when I was going into surgery," she said after her op last year (15). "It was totally terrifying to have my whole career in the hands of a surgeon.
"I wasn’t allowed to talk, or make any kind of noise at all, for three weeks. It was insanity inducing... but I was just so scared of doing any more damage that I managed to stay quiet, although I did forget a few times. After the three weeks of silence, no one could shut me up!"