The agency will continue to operate under the same name and Justin Hayward will remain managing director.
The purchase follows Indicia's acquisition of Linnaeus Consulting, a customer engagement agency specialising in digital and mobile channels, in June 2010.
Make It Rain was founded by former Latitude director Justin Hayward in September 2008, and numbers among its clients The Carphone Warehouse and David Lloyd health clubs.
Ian Stockley, managing director of Indicia, said: "The direct marketing industry is evolving rapidly, with social media playing an increasingly important role in the way brands build and shape one-to-one customer relationships.
"There is a natural fit between the two agencies, with Make It Rain having a proven track record of delivering highly responsive search and social media campaigns for its clients, planned and underpinned by a deep understanding of customer behaviours. We are really excited about the benefits this will bring to our clients."
Hayward said: "We're always looking to push the boundaries in everything we do. A greater breadth of customer intelligence is key to continuing our offering of the best service and results in the market.
"Indicia's customer intelligence focus will provide additional insight into our delivery of highly targeted campaigns for all our clients, and keep our digital services at the forefront. Joining Indicia will really serve to aid our growth in 2011."