Filed Pursuant to Rule 424(b)(3)
Registration No. 333-217481

PROSPECTUS SUPPLEMENT NO. 1

(to prospectus dated December 1, 2017)

Ultra Petroleum Corp.

65,600,813 Common Shares

This prospectus supplement is being filed to update and supplement information contained in the prospectus dated December 1, 2017, covering the offer and resale of up to an aggregate of 65,600,813 common shares, no par value, of Ultra Petroleum Corp. by the selling stockholders identified in the prospectus, with information contained in our Current Report on Form 8-K, filed with the Securities and Exchange Commission on December 1, 2017.

This prospectus supplement updates and supplements the information in the prospectus and is not complete without, and may not be delivered or utilized except in combination with, the prospectus, including any amendments or supplements thereto. This prospectus supplement should be read in conjunction with the prospectus and if there is any inconsistency between the information in the prospectus and this prospectus supplement, you should rely on the information in this prospectus supplement.

Investing in our common shares involves a high degree of risk. Before buying any common shares, you should carefully read the discussion of material risks of investing in our common shares in “Risk Factors” beginning on page 3 of the prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Prospectus Supplement dated December 1, 2017

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event Reported): December 1, 2017 (December 1, 2017)

ULTRA PETROLEUM CORP.

(Exact Name of Registrant as Specified in Charter)

400 N. Sam Houston Parkway E.

Suite 1200

Houston, Texas 77060

(Address of Principal Executive Offices) (Zip Code)

281-876-0120

(Registrant’s telephone number, including area code)

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR §230.405) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR §240.12b-2). Emerging growth company  ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

Ultra Petroleum Corp. (the “Company”) is filing this Current Report on Form 8-K to announce that Patrick Ash, Vice President, Development, has accepted a new position at a larger company. As a result, he is resigning his employment with us effective at the close of business today.

“Patrick has been a valued member of our management team for many years, we greatly appreciate his efforts on behalf of the Company, and we wish him every success in the future,” said Michael D. Watford, Chairman, President and Chief Executive Officer of the Company.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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