O’Shea, who had been Centrica's chief financial officer since 2018, replaces Iain Conn, who left the energy company last month.
READ: British Gas owner Centrica weak as it cancels dividend as coronavirus pandemic hits gas demand
Conn’s departure was agreed last summer after a slump into deep losses and a dividend cut with the FTSE 100-listed company shedding two-thirds of its value under his leadership.
In a statement, the company said O’Shea will be paid “in line with Centrica's current remuneration policy and practice”, with a base salary of £775,000.
The group noted that it is now looking for a new chief financial officer.
Shares dipped 1% to 35.25p on Tuesday morning.