There is no direct bus running from Delhi to Leh. You have to change buses about three times. Firstly, you have to take a bus from Delhi to Manali, then from Manali to Keylong and then lastly you have to catch a bus from Keylong to Leh.
It will be a long journey so you can even stay for a night at Manali and Keylong from where you have to change the buses. This will also help you in better acclimatization.
No direct bus. The Delhi to Leh bus is a bus service run by HRTC from Delhi to Leh via Manali. This service starts after the Manali – Leh highway reopens for the season and is declared by the authorities as safe for a Bus to ply. It remains available from Mid-June to September. After this, the service is suspended until next year. The total duration of the journey is approximately 52 hours. The actual travel time is close to 35 hours (excluding the night stay at Keylong). This bus covers a total of over 1100 km through some of the most challenging roads, and 5 high-altitude passes. It is an extension of the Delhi to Keylong route; which was later extended till Leh. The bus runs through six different states or UTs – Delhi, Haryana, Punjab, Chandigarh, Himachal Pradesh, Jammu & Kashmir. It covering the plains of Haryana & Punjab, the lush green landscapes of Kullu-Manali, adventurous roads midst snow-covered peaks of 5 high altitude passes, and beautiful vistas of the cold desert of Leh-Laddakh.