Less than a week after emerging as a big investor in Sysco, the activist investor Nelson Peltz has gained seats on the food service company’s board.

Sysco said on Thursday that it had added Mr. Peltz and Josh Frank, another executive at Trian Fund Management, as its newest corporate directors, avoiding a potential fight over its board.

The move is the latest win for Mr. Peltz in a long career of shareholder activism, an approach to investing in which firms buy stakes in companies and then push for changes in strategy. Activist investors have gained enormous influence over corporate America over the last decade, as mutual funds and other shareholders have increasingly backed efforts to drive up the stock prices of underperforming companies.

Mr. Peltz has taken on the likes of PepsiCo and Mondelez International, though he has preferred to settle with companies and gain director seats instead of waging protracted fights for board representation.