As an amateur, Leona Maguire held the world No.1 ranking longer than anybody else – 135 weeks in total between May 2015 and February 2018 - although that record was broken by Rose Zhang in April 2023. Alongside her twin sister Lisa she represented Europe in both the Junior Ryder Cup – a mixed event – and two Junior Solheim Cups before they both turned professional in 2018.
A highlight of Maguire's amateur career was lifting the Smyth Salver at the 2016 AIG Women's Open at Woburn, finishing in a tie for 25th.
Her joint sixth at the 2021 Evian Championship was highlighted by a closing 10-under 61, which equalled the lowest-ever round in a major by a man or woman set two days earlier by Jeong-eun Lee. That led to a first Solheim Cup cap as a wild card pick by captain Catriona Matthew and in Europe’s dramatic victory she was the star of the show, earning 4½ points out of a possible five. It was the best-ever performance by a cup rookie.
Her major progress continued in 2022, as she posted a career-best major finish in the AIG Women's Open at Muirfield, tying for fourth place. Her final round of 66 included an eagle on the par-5 fifth hole, and was the lowest of the Sunday.
Maguire is also a two-time winner on the LPGA Tour, having won the 2022 Drive On Championship and this year's Meijer LPGA Classic.