The deal was announced in July, but was subject to regulatory approval.
The buy is Walstead’s fourth major continental acquisition in three years and will propel overall sales at the group to around €730m (£650m).
Walstead said the deal cemented the UK-headquartered group's position as “the largest independent web offset printer of retail advertising flyers and magazines in Europe”. Chairman Mark Scanlon said the firm would issue a trading update at the end of this month.
LSC Poland is being rebranded as Walstead CE. The operation had sales of €210m last year and employs more than 2,000 staff across its six sites in Poland. It runs 23 web presses and five sheetfed presses, and prints a range of products including magazines, catalogues, directories and retail flyers.
The terms of the deal were not disclosed, although LSC Communications (formerly RR Donnelley) said at the time of the disposal that the transaction would reduce its debt by approximately $60m (£46m), “using a combination of sale proceeds and repatriated cash”.