Methold, who has been at BBH for the past six years, is currently negotiating her exit from the agency.
During her stint there she produced the Lynx Pulse campaign, which generated a number-one single, and worked with the directors Tony Scott and Martin Scorsese on the agency's Johnnie Walker "keep on walking" ad.
The appointment will reunite Methold with the W&K creative directors, Tony Davidson and Kim Papworth. The trio worked together at Leagas Delaney and BMP DDB.
Methold said: "I've known Tony and Kim for 15 years and I think they're doing great work at W&K. It's a smaller place with a very different way of working and hopefully this will enable me to get a bit more involved in creative development."
Methold replaces Steiner, who left W&K in July this year to go to Grey, ending the agency's 17-month wait for a head of television.