Reporting to chief executive Alistair Buchanan, Harrison leads a team of around 60 people.
She is responsible for the division's offices in London and Glasgow and is charged with enforcement and compliance, corporate governance, licensing and industry code modifications.
She also takes charge of government relations, consumer affairs and 'fuel poverty' policy.
Harrison's appointment follows the departure of MD of corporate strategy Dr Boaz Moselle, who is joining management consultancy The Brattle Group to head its new Brussels office.
Gas and electricity companies are in the media spotlight for increasing bills at a faster rate than wholesale price increases.
Consumer watchdog Energywatch received more than 40,000 complaints from consumers last year - mostly related to overcharging - and has filed a 'super-complaint' with the industry regulator, which is responsible for promoting competition.
Ofgem has opened an investigation, due to end in July, into overcharging, after Energywatch alleged some companies were ripping off customers.
The probe will also examine whether the complexity of bills prevents consumers from making informed decisions about suppliers.
Harrison joined Ofgem in September 1999.