Nicole Melichar-Martinez (née Melichar; Czech: Nicole Melicharová, Czech pronunciation: [ˈmɛlɪxarovaː]; born July 29, 1993) is an American professional tennis player who specializes in doubles. On 3 July 2023, she peaked at world No. 6 in the WTA doubles rankings. Melichar won a title in mixed doubles at the 2018 Wimbledon Championships with Austrian partner Alexander Peya. She has also won 17 WTA Tour doubles titles as well as two 125 titles on the WTA Challenger Tour.

In singles, she has reached a career-high singles ranking of No. 400 in 2012 and has won two ITF titles.

Melichar is a two-time Grand Slam tournament finalist in women's doubles, finishing runner-up at the 2018 Wimbledon Championships with Květa Peschke and the 2020 US Open with Xu Yifan.

Melichar made her Fed Cup debut for the U.S. team in 2019, partnering Danielle Collins, losing their match against Australian pair of Ashleigh Barty and Priscilla Hon.

She also reached four WTA 1000 finals, at the Cincinnati Open in 2020 with Xu Yifan, and in 2022 and 2023 with Ellen Perez, and at the 2022 Canadian Open also with Perez.

Melichar-Martinez qualified for the third time at the WTA Finals in 2023, partnering Ellen Perez and reached the semifinals for the second time, having made it to that level also in 2021 with a different partner, Dutch player Demi Schuurs. Next the pair Melichar/Perez reached the final, a first time at this level for both players. They lost to Laura Siegemund and Vera Zvonareva in the championship match.

At the 2024 Dubai Championships, she reached her fifth WTA 1000 final with Perez, before losing to fourth seeds Storm Hunter and Kateřina Siniaková. As top seeds, they won the 2024 Bad Homburg Open, defeating Chan Hao-ching and Veronika Kudermetova in the final.

Melichar-Martinez and Perez qualified for the 2024 WTA Finals and reached the semifinals after compiling a record of two wins and one loss in the group stages. They lost in the last four to second seeds Gabriela Dabrowski and Erin Routliffe, in straight sets.