In 1967, Tyndall joined Chesterton's newly founded National Front (NF) and became its leader in 1972, overseeing growing membership and electoral growth. His leadership was threatened by various factions within the party which eventually led to him losing his position as leader in 1974. He resumed this position in 1975, although the latter part of the 1970s saw the party's prospects decline. Following an argument with long-term comrade Martin Webster, Tyndall resigned from the party in 1980 and formed his short-lived New National Front (NNF). In 1982, he merged the NNF into his own newly formed British National Party (BNP). Under Tyndall, the BNP established itself as the UK's most prominent extreme-right group during the 1980s, although electoral success eluded it. Tyndall's refusal to moderate the BNP's policies or image caused anger among a growing array of "modernisers" in the party, who ousted him in favour of Nick Griffin in 1999. In 2005, Tyndall was charged with incitement to racial hatred for comments made at a BNP meeting. He died two days before his trial was due to take place.