Brown Brothers Harriman & Co. has hired two new investment executives to help bolster the private equity leadership team, BBH announced Wednesday.

Suzanne Brenner will join the firm as managing director and chief investment officer. She will lead the BBH Private Banking Investment Research Group, which is responsible for manager selection, capital allocation and investment decisions across the firm’s private banking client portfolio. She previously was with the Metropolitan Museum of Art.

Donald Hardie, a long-time private equity investor, has joined the firm as managing director and portfolio manager within the BBH Capital Partners private equity investment team. He will help spearhead an expansion of the capital partners platform focused on investments in lower middle-market companies. Since 2009, Hardie led private investments for a single-family office based in Greenwich, Conn., where he was a partner