The merger was not considered a monopoly, the Office of Trade Competition Commission (OTCC) said, without giving further details.
Tesco said earlier this year it had agreed to sell its supermarket businesses in Thailand and Malaysia to Charoen Pokphand Group for an enterprise value of $10.6 billion..
Britain's biggest retailer has nearly 2,000 Thai retail outlets, many of which it bought from CP Group during the 1997-8 Asian financial crisis.
The latest proposed change of ownership follows a tussle between three of Thailand's most famous retail billionaires. Dhanin Chearavanont's CP Group runs its 12,000 7-Eleven convenience stores through CP All and about 80 cash-and-carry stores under Siam Makro.
CP Group did not immediately respond to a request for comment. Tesco noted the antitrust regulator's statement and said it was waiting for CP Group to receive the formal regulatory approval notice from the OTCC.
Lawyers and analysts said earlier this year there was a possibility the regulator could block the transaction should it find it would create a monopoly or market dominance.
The OTCC's approval on Friday came with conditions that CP Group could not strike another retail merger deal over the next three years.
It also carried stipulations that information about suppliers not be shared between CP's stores and that products from small- and medium-sized firms see higher sales over the next five years via the outlets under the group's control.
Tesco had been expecting to complete the sale of its Thailand and Malaysia businesses this year.
Its new chief executive, Ken Murphy, last month said there were no plans for further retrenchment from overseas markets.
(Writing by Martin Petty; Editing by Kirsten Donovan)
By Patpicha Tanakasempipat