Incumbent Popcorn - whose clients include Babybel group Bel UK and Panasonic - won the account in January last year, but did not take part in the recent competive pitch for the account, agency MD Louise Lloyd said.
Brand2Life's remit includes raising awareness of Moonpig as "an everyday destination for personalised cards, flowers and gifts, and not just big calendar events", the agency said in a statement.
Brands2Life joint consumer MD Alex Williams told PRWeek: "We want to broaden people's knowledge of the Moonpig product range to help them celebrate everyday moments."
To generate awareness of the range, which includes bouquets of flowers, bottles of champagne, and novelty items, the agency will launch a series of integrated campaigns throughout the year and leverage social media trends to promote products, Williams added.
"Our remit also includes evolving perceptions of the brand and engaging with new audiences who haven't considered Moonpig before, for example, people who still shop for cards on the high street, and those who only visit the site to send cards."
Williams said this would help Moonpig stand out in a crowded marketplace.
Founded in 2000, Brands2Life is the UK's 25th largest agency, according to the 2017 PRWeek UK Top 150 rankings table. Other clients include LinkedIn, Groupon and Virgin Media. It launched its first US office in San Francisco in January.