Inclusion Criteria:

• Have a diagnosis of IPF within the previous 5 years from time of screening and confirmed at baseline
• FVC >/=40 % and less than or equal to (
• Stable baseline lung function as evidenced by a difference of less than (<) 10% in FVC (liters) measurements between screening and Day 1/Visit 2 prior to randomization
• Diffusion capacity of the lung for carbon monoxide >/=25% and
• Ability to walk >/=100 meters unassisted in 6 minutes
• Cohort A: No background IPF therapy for >/=4 weeks allowed prior to randomization and throughout the placebo-controlled study period
• Cohort B: Tolerated dose of pirfenidone /=4 weeks required prior to randomization and throughout the placebo-controlled study period

Exclusion Criteria:

• History of severe allergic reaction or anaphylactic reaction to a biologic agent or known hypersensitivity to any component of the lebrikizumab injection
• Evidence of other known causes of interstitial lung disease (ILD)
• Lung transplant expected within 12 months of screening
• Evidence of clinically significant lung disease other than IPF
• Post bronchodilator forced expiratory volume in 1 second (FEV1)/FVC ratio < 0.7 at screening
• Positive bronchodilator response, evidenced by an increase of >/=12% predicted and 200 milliliters (mL) increase in FEV1 or FVC
• Class IV New York Heart Association chronic heart failure or historical evidence of left ventricular ejection fraction <35%
• Hospitalization due to an exacerbation of IPF within 4 weeks prior to or during screening
• Known current malignancy or current evaluation for potential malignancy
• Listeria monocytogenes infection or active parasitic infections within 6 months prior to randomization
• Active tuberculosis requiring treatment within 12 months of screening
• Known immunodeficiency, including but not limited to human immunodeficiency virus (HIV) infection
• Past use of any anti-interleukin (IL)-13 or anti-IL-14/IL-13 therapy, including lebrikizumab
• Evidence of acute or chronic hepatitis or known liver cirrhosis

Exclusions Limited to Cohort B:

• Known achalasia, esophageal stricture, or esophageal dysfunction sufficient to limit the ability to swallow oral medication
• Tobacco smoking or use of tobacco-related products within 3 months of screening or unwillingness to avoid smoking throughout the study period
• Known or suspected peptic ulcer
• Any condition that, as assessed by the investigator, might be significantly exacerbated by the known side effects associated with pirfenidone
• Creatinine clearance <40 mL/minute, calculated using the Cockcroft-Gault formula
• Use of following therapies within 4 weeks of randomization (Day 1/Visit 2) or during the study
• Strong inhibitors of CYP1A2 (Cytochrome P450 family 1 subfamily A member 2) (example: fluvoxamine or enoxacin)
• Moderate inducers of CYP1A2 (limited to tobacco smoking and tobacco-related products)