Howell has chosen to step down after six years as CEO.
Mostrey joined Euroclear in 2010 as executive director and chief technology and services officer.
She also served as a member of the group’s management committee, executive director of the board, and chair of several of the group’s central securities depositories.
Previously, Mostrey gained experience as a non-executive director of SWIFT, Euronext and RealDolmen.
Marc Antoine Autheman, chair of Euroclear Group, said: “The board congratulates Lieve Mostrey on her appointment to CEO. Lieve brings to the role vast experience both within Euroclear as well as from earlier roles in financial services and non-executive board directorships.”
“The board also thanks Tim Howell for Euroclear’s success achieved during his tenure; building its business, forging new business partnerships, growing shareholder returns and strengthening the organisation’s resilience as a key financial market infrastructure.”
Mostrey, CEO of Euroclear Group, said: “As the financial industry’s trusted provider of post-trade services, Euroclear is entering an exciting new phase of its development, amid the evolution of global capital markets. I look forward to leading Euroclear’s team of dedicated employees, committed to delivering risk-mitigation, automation and efficiency at scale for our global client franchise.”