Playing with Ulrikke Eikeri, Grammatikopoulou reached her first WTA Tour doubles final at the 2021 Lausanne Open, losing to Susan Bandecchi and Simona Waltert in a deciding champions tiebreak.

[6] Grammatikopoulou qualified for her second Grand Slam tournament at the 2022 French Open,[7] losing in the first round to wildcard entrant Daria Saville.

[8] In August 2022, Grammatikopoulou won her biggest singles title to date at the WTA 125 Vancouver Open, defeating Lucia Bronzetti in the final.

[9] Partnering Despina Papamichail, she won her first WTA 125 doubles title at the 2023 Barranquilla Open, overcoming Yuliana Lizarazo and María Paulina Pérez García in the final.

[10][11] Only main-draw results in WTA Tour, Grand Slam tournaments, Fed Cup/Billie Jean King Cup and Olympic Games are included in win–loss records.