Abbott will arrive at Lord’s, subject to Cricket South Africa clearance, after the IPL and will be available from May 28 until the start of his country’s tour of Bangladesh a month later.
Abbott, who played for Hampshire in last year’s competition, has eight Twenty20 international caps and impressed for South Africa during the recent World Cup.
“I am delighted to have signed for Middlesex for the T20 campaign,” said the 27-year-old.
“I enjoyed my time in England last year immensely and I am looking forward to a new and exciting challenge with Middlesex. It is an honour to have signed for such an illustrious club, and I look forward to pulling on the shirt for the first time.”
Abbott has been a long-term target for Middlesex and managing director of cricket Angus Fraser admits he is planning how to replace him for the latter stages of the competition.
“During the winter we identified that our priority for a second T20 Blast player was a high-quality fast bowler, and we believe in Kyle we have signed someone who will significantly strengthen our T20 side.
“Kyle continues to highlight what a top bowler he is. He was exceptional during the recent World Cup, where he took nine wickets in four games at an average of 14 and conceded just over four runs per over. In a high scoring tournament these were outstanding figures.
“It is unfortunate we cannot have him for the entire tournament, but we are not the only county to have these issues. With this in mind, we are already speaking to people about Kyle’s replacement for the final six group T20 Blast matches.”