Mr Johnson senior, a former Euro MP, joined his son, 54, at the event in Exeter, Devon, which is not far from his Somerset home.
They posed for photographs outside the Sandy Park Conference Centre close to the city’s rugby stadium.
Later there was applause for Mr Johnson senior and also rival Jeremy Hunt’s sister and her children, who were also in the audience.
Hair care bunch: Stanley Johnson joined his son Boris (right) at the Tory leadership hustings in Exeter, Devon, today.
The former MEP arrived heavily laden with baggage and wearing a bold burnt orange blazer at Sandy Park Conference Centre close to the city’s rugby stadium.
Supporters of both Conservative Party leader contenders, Boris Johnson and Jeremy Hunt, flanked the entrance to Sandy Park Conference Centre in Exeter ahead of the event.
Pro-Boris supporters were giving out blue ‘back Boris badges’ and those in favour of his rival were handing out leaflets explaining ‘Why it has to be Hunt’.
Journalists were told there will be standing-room only in the venue as all seats will be taken by party members.
Organisers said there were an estimated 800 people in the audience.