Harrison has joined MoFo's London office, leaving just two dual-qualified US finance partners in Weil's London office.
The move comes after MoFo raided Weil for corporate partners Paul Claydon and James Gubbins in January. Weil also lost debt practice counsel John Markland to Kirkland & Ellis in May last year.
Weil launched its UK finance practice in 1995 when it took Maurice Allen and his team from Clifford Chance, but it subsequently lost the team to White & Case in 2000.
Harrison was headhunted to lead MoFo in its development of a UK law finance practice to support the firm's existing finance practices in the US and Asia.
City-based US finance partner Brian Bates said Harrison would act for financial institutions, sponsors and governments on complex domestic and cross-border financial transactions under English law.
"With Chris joining us, we've now added a top-notch UK law finance capability which complements London's corporate practice and further strengthens our ability to handle global corporate finance matters," said Bates.
Weil Gotshal London managing partner Mike Francies said: "We have a small but good debt practice. We'll be looking to recruit more people to the team but only if they are the right people.
"If you look at the work we've done over the past three years, Richard Ginsburg has been the leading partner on most of it."