Silver City Tech sent more than three million unsolicited messages to people across the UK in five months, the Information Commissioner's Office (ICO) said.
The Dorset-based firm was probed as part of an investigation prompted by complaints about nuisance texts.
Oracle Insurance Brokers, which sent 136,000 texts, was also fined £30,000.
'Like postmen'
Bournemouth-based Silver City Tech, and London firm Oracle Insurance Brokers, sent messages inviting people to apply for short-term loans.
An example of the type of message Silver City Tech sent is: "Maxine, we have received your details and could arrange £500 over six months. Click for cash. 1270% rep APR, 292% int. Stop2 opt out."
Both companies told ICO investigators it was a third party company which had sent the texts on their behalf - a practice known as affiliate marketing.
However, it was the firms' responsibility to check that the recipients had specifically consented to receiving marketing texts, the watchdog said.
Andy Curry, ICO enforcement group manager, said: "Affiliate firms are like postmen, delivering the message.
"It's the people behind the message whose job it is to make sure it complies with the law."
A firm which sent millions of spam texts offering easy access high-interest loans has been fined £100,000.