The 1975 NASCAR Grand National Winston Cup Series was the 27th season of professional stock car racing in the United States and the 4th season in the modern era of the NASCAR Cup series. The season began on Sunday, January 19 and ended on Sunday, November 12. Richard Petty, driving the #43 Petty Enterprises STP Dodge scored his sixth NASCAR Grand National Series Winston Cup Championship. Bruce Hill was named NASCAR Rookie of the Year. NASCAR introduced a new points system for 1975, a system designed by statistician Bob Latford. For the first time, each race on the NASCAR Winston Cup Grand National schedule carried an equal point value, a system that would be used for 36 seasons, from 1975 to 2010, with modifications in 2004 and 2007 each time by increasing the emphasis for a win in adding five additional points each time for a race winner. The original points system ran for the first 29 seasons, from 1975 to 2003.

The 1975 Gwyn Staley 400 took place on April 6 at North Wilkesboro Speedway. The race was dominated by Richard Petty, who led a total of 311 laps and won by a margin of over three laps.

The 1975 Nashville 420 took place on July 20 at Nashville Speedway. Cale Yarborough dominated the race after passing Walter Ballard on lap 50, leading the rest of the laps afterwards and winning.

Current rules state a black flag assessed at the end of the race results in a time penalty, primarily for driving standards or track limits. This was assessed on Ricky Rudd at Sonoma in 1991 (inappropriate contact), Chase Briscoe at Indianapolis in 2021 (track limits, then inappropriate contact when under penalty), or Shane van Gisbergen at Austin in a second tier series race in 2024 (exceeded track limits in Maggots-Becketts-Chapel on final lap).

(key) Bold – Pole position awarded by time. Italics – Pole position set by owner's points. * – Most laps led.