The superstar performed her song "XO" at the top of the Staples Center memorial, backed by a choir and a small orchestra, explaining it was one of Kobe's "favourite songs".
"I'm here 'cause I love Kobe," she told the packed venue, where the sportsman played for the Los Angeles Lakers.
Dressed in a gold suit, Beyonce also performed a stirring rendition of her hit "Halo".
The memorial started 30 minutes late to allow thousands of fans to file in to the Staples Center.
Kobe and Gianna were remembered at the event, alongside the other seven people who also perished in a helicopter crash last month (January 2020).
The Celebration of Life also featured highlight clips of Kobe's basketball career and his life with his family, beamed onto the Staples Center's famous jumbotron screens.
Kobe's friend Jimmy Kimmel served as the event's MC, but confessed he was the "wrong person" to lead the memorial as he sobbed while honouring his late friend and the victims of the crash, although he also managed a few laughs as he poked fun at the Lakers' rivals, the Boston Celtics.
Kobe's wife, Vanessa, also took the stage to thank fans and friends for their support. Dressed all in black and fighting back tears, she said, "Thank you all so much for being here. It means so much to us..."
"The outpouring of love and support that my family has felt from around the world has been so uplifting. Thank you so much for all your prayers..."
She went on to talk about her "baby girl Gigi", calling her an "amazingly sweet and thoughtful soul", adding, "She was daddy's girl but I know she loved her momma... She was one of my very best friends."
"Kobe always said she was me; she had my fire, my personality and sarcasm, but she was tender and loving on the inside. She had the best laugh. It was infectious. It was pure and genuine... Gigi was sunshine, she brightened up my day, every day."
Vanessa added, "We will not be able to see Gigi go to high school... and ask her how her day went; we didn't get the chance to teach her how to drive a car; I won't be able to tell her how gorgeous she looks on her wedding day; I'll never get to see my baby girl walk down the aisle, have a father-daughter dance with her daddy... or have babies of her own. Gianna would have been an amazing mommy. Gianna would have probably become the best player in the WNBA (Women's National Basketball Association). She would have made a huge difference for women's basketball."
Turning her attention to her late husband, Vanessa called Kobe "my soulmate", adding, "To me, he was Ko-ko, my boo boo, my bae-boo... I couldn't see him as a celebrity, nor just an incredible basketball player; he was my sweet husband and the beautiful father of my children. He was mine. He was my everything."
"I was his first girlfriend, his first love, his wife, his best friend, his confidante and his protector. He was the most amazing husband. Kobe loved me more than I could ever express... we balanced each other out..."
Recalling his thoughtful and romantic Valentine's Day gifts, Vanessa told fans and friends, "He bought me the actual notebook and the blue dress Rachel McAdams wore in 'The Notebook' movie... We had hoped to grow old together, like the movie."
"A couple of weeks before they passed, Kobe sent me a sweet text and mentioned how he wanted to spend time together, just the two of us, without our kids, because I'm his best friend first. We never got the chance to do it... But I'm thankful I have that recent text. It means so much to me."
"Kobe wanted us to renew our vows... and he wanted to travel the world together."
Vanessa also lightened proceedings when she called her late husband the "MVP of girl dads", explaining, "He never left the toilet seat up."
She added, "I want my daughters to know and remember the amazing person, husband and father he was; the kind of man that wanted to teach the future generations to be better and keep them from making his own mistakes... He taught us all valuable lessons about life and sports."
Tearing up at the end of her speech, Vanessa told the Staples Center crowd that God knew Kobe and Gigi couldn't exist without each other, adding, "He had to bring them home to have them together. Babe, you take care of our Gigi... We love and miss you Boo Boo and GiGi. May you both rest in peace and have fun in heaven until we meet again one day."
She received a standing ovation as she walked off the stage.
Other speakers included basketball stars Diana Taurasi, Sabrina Ionescu, college basketball coach Geno Auriemma, who had hoped to welcome Gianna Bryant to his Connecticut Huskies team, and Lakers general manager and Bryant's best friend and former agent Rob Pelinka, who recalled his pal teaching himself to play Beethoven's "Moonlight Senata" on the piano, so he could serenade his wife. Pelinka then introduced Alicia Keys to the stage to play the classical favourite.
Among the mourners were Snoop Dogg, LL Cool J, Spike Lee, Jennifer Lopez, basketball greats Magic Johnson, Dwyane Wade, and Shaquille O'Neal, and current stars Stephen Curry, Dwight Howard, and James Harden.
The proceeds from ticket sales for the Celebration of Life, which was interspersed with chants of 'Kobe, Kobe, Kobe', will benefit the Mamba & Mambacita Sports Foundation, which Vanessa relaunched earlier this month.