Xenon Pharmaceuticals Inc.

We have a written code of conduct that applies to all of our directors, officers and employees. A copy of the most up-to-date version of our code of conduct is available within the “Investors” section on our company website located athttp://www.xenon-pharma.com and on SEDAR+ atwww.sedarplus.ca. We will post amendments to our code of conduct or waivers of the same for directors and executive officers on the “Investors” section on our website located athttps://www.xenon-pharma.com.

Rule 10b5-1 Trading Plans

From time to time, our officers, as defined in Rule 16a-1(f), and directors may enter into Rule 10b5-1 ornon-Rule 10b5-1 trading arrangements, as each term is defined in Item 408 or Regulation S-K. During the quarter ended December 31, 2025, each of our officers listed in the table below adopted a Rule 10b5-1 trading arrangement intended to qualify as a "plan providing for eligible sell-to-cover transactions" under Rule 10b5-1(c)(1)(ii)(D)(3) under the Exchange Act. The trading arrangements are in the form of durable sell-to-cover instructions that provide for sales of common shares necessary to satisfy such individual’s tax withholding obligations incurred in connection with the vesting or settlement of restricted share units and performance share units previously granted or that could in the future be granted by the Company, whether vesting is based on the passage of time or the achievement of performance goals. The total number of shares of common shares that may be sold pursuant to the sell-to-cover instructions is not determinable and the sell-to-cover instructions will remain in place indefinitely unless revoked in writing.

(1)

The trading arrangements will apply to the first award of RSUs granted to the applicable officer on or after March 12, 2025; the first award of PSUs granted to such officer on or after March 11, 2024; and any RSUs or PSUs that may, from time to time following either such date, be granted to such officer by the Company, other than (i) the portion of any RSU or PSU award that vests prior to the expiration of the applicable cooling-off period as set forth in such officer’s trading arrangement, and (ii) any future granted RSUs or PSUs which by the terms of the applicable award agreement require us to withhold shares for tax withholding obligations in connection with the vesting and settlement of such RSUs or PSUs, as applicable, and therefore do not permit sell-to-cover transactions. The number of shares sold under these elections will vary based on the tax withholding obligations incurred upon vesting.

Compensatory Arrangements of Certain Officers

On February 26, 2026, the Company entered into an amended and restated employment agreement with each of Ian Mortimer, the Company’s President & Chief Executive Officer; Tucker Kelly, the Company’s Chief Financial Officer; Darren Cline, the Company's Chief Commercial Officer; Andrea DiFabio, the Company’s Chief Legal Officer and Corporate Secretary; and Christopher Kenney, the Company’s Chief Medical Officer. Pursuant to the amended and restated employment agreements, each officer received an increase to his or her annual base salary effective as of January 1, 2026 (Mr. Mortimer: $820,000; Mr. Kelly: $550,000; Mr. Cline: $545,000; Ms. DiFabio: $530,000, Dr. Kenney: $590,000) and each of Mr. Mortimer, Ms. DiFabio, and Dr. Kenney received an increase to his or her annual target bonus (the "Target Bonus Amount"), expressed as a percentage of base salary (Mr. Mortimer: 70%; Ms. DiFabio: 45%; Dr. Kenney: 45%).

Each of the amended and restated employment agreements with Mr. Mortimer, Mr. Kelly, Mr. Cline, Ms. DiFabio, and Dr. Kenney provides that if we terminate the applicable executive’s employment without cause (in the cases of Mr. Kelly, Mr. Cline, Ms. DiFabio and Dr. Kenney, as such term is defined in the executive’s employment agreement) outside of the period beginning three months before a Change of Control (as such term is defined in the executive’s employment agreement) and ending 12 months after the Change of Control, we will provide, subject to the receipt of a release of all claims, (i) in the case of Mr. Mortimer, a working notice of termination (in which case all terms and conditions of employment including compensation and benefits, subject to the applicable insurer’s terms of coverage, will continue), base salary continuance, a lump sum payment of base salary, or an equivalent combination of any of the foregoing, for 18 months (such number of months, the “Mortimer Payment Period”), and in the cases of Mr. Kelly, Mr. Cline, Ms. DiFabio and Dr. Kenney, a lump sum severance payment equal to the executive’s base salary for a number of months equal to 12 months plus one additional month for every one year of consecutive service (up to a combined maximum of 18 months) (such number of months, the “Payment Period”); (ii) a lump sum payment equal to the executive’s target annual bonus for the fiscal year in which the termination of employment occurs, pro-rated based on the number of days the executive was employed during such fiscal year (the “Pro-Rated Annual Bonus”); (iii) in the case of Mr. Mortimer, continued coverage for the executive under our group benefits insurance, or payment of the cost of monthly premiums under our group benefits insurance, until the end of the 18-month period following his termination of employment or the date on which he commences full-time employment; (iv) in the cases of Mr. Kelly, Mr. Cline, Ms. DiFabio, and Dr. Kenney, Company payment of the employer portion of COBRA premiums for the Payment Period, subject to the executive’s eligibility for, and timely election of, COBRA coverage; (v) payment to the executive of an amount equal to the contributions for retirement savings that we would have paid on his or her behalf for the Mortimer Payment Period or the Payment Period, as applicable; and (vi) continued vesting of stock options, restricted stock units, other equity or equity-based awards, and any other deferred compensation granted to the executive for three months following the date the executive’s employment terminates and continued exercisability of such options and deferred compensation for up to six months following termination of employment.

If, during the change of control period, the executive’s employment is terminated without cause or the executive resigns for Good Reason (as such term is defined in the executive’s employment agreement), we will, subject to the receipt of a release of all claims, (i) pay the executive a lump sum amount equal to the product obtained by multiplying (A) the sum of his or her base salary plus his or her target annual bonus by (B) the number of months in the Payment Period divided by 12 (or in the case of Mr. Mortimer, by two); (ii) pay the executive the Pro-Rated Annual Bonus; (iii) pay the executive an amount equal to the contributions for retirement savings that we would have paid on his or her behalf for the Payment Period (or in the case of Mr. Mortimer, for 24 months); (iv) fully accelerate the vesting of all of the executive’s unvested stock options, restricted stock units, other equity or equity-based awards (with any performance-based awards vesting in full), and other deferred compensation awards; (v) provide for the continued exercisability of the executive’s stock options for the longer of (A) six months from the termination of the executive’s employment or (B) the period stipulated in the applicable plan or grant; (vi) in the case of Mr. Mortimer, arrange for continued coverage under our group benefits insurance, or payment of the cost of monthly premiums under our group benefits insurance, until the end of the 24-month period after the termination of his employment or until he commences full-time employment; and (vii) in the cases of Mr. Kelly, Mr. Cline, Ms. DiFabio, and Dr. Kenney, Company payment of the employer portion of COBRA premiums for the Payment Period, subject to the executive’s eligibility for, and timely election of, COBRA coverage.