Tegan was the longest-serving companion in terms of years on the series (3 years, 1 month), closely followed by Sarah Jane Smith, although Jamie McCrimmon was in the most episodes and stories.
Tegan was the longest-serving companion in terms of years on the series (3 years, 1 month), closely followed by Sarah Jane Smith (whom Tegan briefly meets in the serial The Five Doctors). However, Jamie McCrimmon was in the most episodes and stories.